Merge "Create class to diff ChangeInfos for the REST API"
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 91fe24b..23720460 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -5189,6 +5189,13 @@
 +
 By default 50.
 
+[[suggest.skipServiceUsers]]suggest.skipServiceUsers::
++
+If link:access-control.html#service_users[service users] should be skipped when
+suggesting reviewers.
++
+By default true.
+
 [[tracing]]
 === Section tracing
 
diff --git a/Documentation/dev-bazel.txt b/Documentation/dev-bazel.txt
index 9d29980..8197550 100644
--- a/Documentation/dev-bazel.txt
+++ b/Documentation/dev-bazel.txt
@@ -41,14 +41,8 @@
 [[java]]
 === Java
 
-==== MacOS
-
-On MacOS, ensure that "Java for MacOS X 10.5 Update 4" (or higher) is installed
-and that `JAVA_HOME` is set to the
-link:install.html#Requirements[required Java version].
-
-Java installations can typically be found in
-"/System/Library/Frameworks/JavaVM.framework/Versions".
+Ensure that the link:install.html#Requirements[required Java version]
+is installed and that `JAVA_HOME` is set to it.
 
 To check the installed version of Java, open a terminal window and run:
 
diff --git a/Documentation/dev-rest-api.txt b/Documentation/dev-rest-api.txt
index fec9c97..a28e230 100644
--- a/Documentation/dev-rest-api.txt
+++ b/Documentation/dev-rest-api.txt
@@ -50,6 +50,11 @@
  curl -X PUT --user john:2LlAB3K9B0PF --data-binary @project-desc.txt --header "Content-Type: application/json; charset=UTF-8" http://localhost:8080/a/projects/myproject/description
 ----
 
+[[pretty-json]]
+=== Pretty JSON
+
+By default any JSON in responses is compacted. To get pretty-printed JSON add `pp=1` to the request.
+
 === Authentication
 
 To test APIs that require authentication, the username and password must be specified on
diff --git a/Documentation/install.txt b/Documentation/install.txt
index 94a576c..6e1a9bd 100644
--- a/Documentation/install.txt
+++ b/Documentation/install.txt
@@ -10,39 +10,6 @@
 +
 Gerrit is not yet compatible with Java 13 or newer at this time.
 
-[[cryptography]]
-== Configure Java for Strong Cryptography
-
-Support for extra strength cryptographic ciphers: _AES128CTR_, _AES256CTR_,
-_ARCFOUR256_, and _ARCFOUR128_ can be enabled by downloading the _Java
-Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files_
-from Oracle and installing them into your JRE.
-
-[NOTE]
-Installing JCE extensions is optional and export restrictions may apply.
-
-. Download the unlimited strength JCE policy files.
-+
-- link:http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html[JDK7 JCE policy files,role=external,window=_blank]
-- link:http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html[JDK8 JCE policy files,role=external,window=_blank]
-. Uncompress and extract the downloaded file.
-+
-The downloaded file  contains the following files:
-+
-[cols="2"]
-|===
-|README.txt
-|Information about JCE and installation guide
-
-|local_policy.jar
-|Unlimited strength local policy file
-
-|US_export_policy.jar
-|Unlimited strength US export policy file
-|===
-. Install the unlimited strength policy JAR files by following instructions
-found in `README.txt`.
-
 [[download]]
 == Download Gerrit
 
diff --git a/Documentation/js_licenses.txt b/Documentation/js_licenses.txt
index 48e729f..7ef9473 100644
--- a/Documentation/js_licenses.txt
+++ b/Documentation/js_licenses.txt
@@ -247,6 +247,38 @@
 ----
 
 
+[[DefinitelyTyped]]
+DefinitelyTyped
+
+* @types/resize-observer-browser
+
+[[DefinitelyTyped_license]]
+----
+    MIT License
+
+    Copyright (c) Microsoft Corporation.
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE
+
+----
+
+
 [[Polymer-2014]]
 Polymer-2014
 
diff --git a/Documentation/licenses.txt b/Documentation/licenses.txt
index b7cdf8a..5f0fb65 100644
--- a/Documentation/licenses.txt
+++ b/Documentation/licenses.txt
@@ -3204,6 +3204,38 @@
 ----
 
 
+[[DefinitelyTyped]]
+DefinitelyTyped
+
+* @types/resize-observer-browser
+
+[[DefinitelyTyped_license]]
+----
+    MIT License
+
+    Copyright (c) Microsoft Corporation.
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE
+
+----
+
+
 [[Polymer-2014]]
 Polymer-2014
 
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 3a5fb96..f66d430 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -6718,6 +6718,10 @@
 A list of link:#context-line[ContextLine] containing the lines of the source
 file where the comment was written. Available only if the "enable-context"
 parameter (see link:#list-change-comments[List Change Comments]) is set.
+|`source_content_type` |optional|
+Mime type of the file where the comment is written. Available only if the
+"enable-context" parameter (see link:#list-change-comments[List Change Comments])
+is set.
 
 |===========================
 
diff --git a/Documentation/rest-api-config.txt b/Documentation/rest-api-config.txt
index 9764c8a..a8d9b3d 100644
--- a/Documentation/rest-api-config.txt
+++ b/Documentation/rest-api-config.txt
@@ -1839,6 +1839,8 @@
 Whether to enable the web UI for editing GPG keys.
 |`report_bug_url`    |optional|
 link:config-gerrit.html#gerrit.reportBugUrl[URL to report bugs].
+|`instance_id`       |optional|
+link:config-gerrit.html#gerrit.instanceId[Short identifier for this Gerrit installation].
 |=================================
 
 [[index-config-info]]
diff --git a/Documentation/user-search.txt b/Documentation/user-search.txt
index e02dc21..52c282e 100644
--- a/Documentation/user-search.txt
+++ b/Documentation/user-search.txt
@@ -190,6 +190,13 @@
 +
 Changes occurring in projects starting with 'PREFIX'.
 
+[[parentof]]
+parentof:'ID'::
+Changes which are parent to the change specified by 'ID'. Change 'ID' can be
+specified as a legacy numerical 'ID' such as 15183, or a Change-Id that can be
+picked from the commit message. This operator will return immediate parents
+and will not return grand parents or higher level ancestors of the given change.
+
 [[parentproject]]
 parentproject:'PROJECT'::
 +
diff --git a/java/com/google/gerrit/common/data/PatchScript.java b/java/com/google/gerrit/common/data/PatchScript.java
index e3c0ba6..1ba5592 100644
--- a/java/com/google/gerrit/common/data/PatchScript.java
+++ b/java/com/google/gerrit/common/data/PatchScript.java
@@ -34,7 +34,17 @@
   public enum FileMode {
     FILE,
     SYMLINK,
-    GITLINK
+    GITLINK;
+
+    public static FileMode fromJgitFileMode(org.eclipse.jgit.lib.FileMode jgitFileMode) {
+      PatchScript.FileMode fileMode = PatchScript.FileMode.FILE;
+      if (jgitFileMode == org.eclipse.jgit.lib.FileMode.SYMLINK) {
+        fileMode = FileMode.SYMLINK;
+      } else if (jgitFileMode == org.eclipse.jgit.lib.FileMode.GITLINK) {
+        fileMode = FileMode.GITLINK;
+      }
+      return fileMode;
+    }
   }
 
   public static class PatchScriptFileInfo {
diff --git a/java/com/google/gerrit/entities/CachedProjectConfig.java b/java/com/google/gerrit/entities/CachedProjectConfig.java
index 0b755b7..2a94bc8 100644
--- a/java/com/google/gerrit/entities/CachedProjectConfig.java
+++ b/java/com/google/gerrit/entities/CachedProjectConfig.java
@@ -14,19 +14,17 @@
 
 package com.google.gerrit.entities;
 
-import static com.google.common.base.Preconditions.checkState;
-
 import com.google.auto.value.AutoValue;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.flogger.FluentLogger;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.errors.ConfigInvalidException;
-import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.ObjectId;
 
 /**
@@ -37,6 +35,8 @@
  */
 @AutoValue
 public abstract class CachedProjectConfig {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
   public abstract Project getProject();
 
   public abstract ImmutableMap<AccountGroup.UUID, GroupReference> getGroups();
@@ -126,34 +126,10 @@
 
   public abstract ImmutableMap<String, String> getPluginConfigs();
 
-  /**
-   * Returns the {@link Config} that got parsed from the specified {@code fileName} on {@code
-   * refs/meta/config}. The returned instance is a defensive copy of the cached value.
-   *
-   * @param fileName the name of the file. Must end in {@code .config}.
-   * @return an {@link Optional} of the {@link Config}. {@link Optional#empty()} if the file was not
-   *     found or could not be parsed. {@link com.google.gerrit.server.project.ProjectConfig} will
-   *     surface validation errors in case of a parsing issue.
-   */
-  public Optional<Config> getProjectLevelConfig(String fileName) {
-    checkState(fileName.endsWith(".config"), "file name must end in .config");
-    if (getProjectLevelConfigs().containsKey(fileName)) {
-      Config config = new Config();
-      try {
-        config.fromText(getProjectLevelConfigs().get(fileName));
-      } catch (ConfigInvalidException e) {
-        // This is OK to propagate as IllegalStateException because it's a programmer error.
-        // The config was converted to a String using Config#toText. So #fromText must not
-        // throw a ConfigInvalidException
-        throw new IllegalStateException("invalid config for " + fileName, e);
-      }
-      return Optional.of(config);
-    }
-    return Optional.empty();
-  }
-
   public abstract ImmutableMap<String, String> getProjectLevelConfigs();
 
+  public abstract ImmutableMap<String, ImmutableConfig> getParsedProjectLevelConfigs();
+
   public static Builder builder() {
     return new AutoValue_CachedProjectConfig.Builder();
   }
@@ -235,8 +211,15 @@
 
     abstract ImmutableMap.Builder<String, String> projectLevelConfigsBuilder();
 
+    abstract ImmutableMap.Builder<String, ImmutableConfig> parsedProjectLevelConfigsBuilder();
+
     public Builder addProjectLevelConfig(String configFileName, String config) {
       projectLevelConfigsBuilder().put(configFileName, config);
+      try {
+        parsedProjectLevelConfigsBuilder().put(configFileName, ImmutableConfig.parse(config));
+      } catch (ConfigInvalidException e) {
+        logger.atInfo().withCause(e).log("Config for " + configFileName + " not parsable");
+      }
       return this;
     }
 
diff --git a/java/com/google/gerrit/entities/CommentContext.java b/java/com/google/gerrit/entities/CommentContext.java
index c8c8a76..68d779c 100644
--- a/java/com/google/gerrit/entities/CommentContext.java
+++ b/java/com/google/gerrit/entities/CommentContext.java
@@ -20,15 +20,24 @@
 /** An entity class representing all context lines of a comment. */
 @AutoValue
 public abstract class CommentContext {
-  private static final CommentContext EMPTY = new AutoValue_CommentContext(ImmutableMap.of());
+  private static final CommentContext EMPTY = new AutoValue_CommentContext(ImmutableMap.of(), "");
 
-  public static CommentContext create(ImmutableMap<Integer, String> lines) {
-    return new AutoValue_CommentContext(lines);
+  public static CommentContext create(ImmutableMap<Integer, String> lines, String contentType) {
+    return new AutoValue_CommentContext(lines, contentType);
   }
 
   /** Map of {line number, line text} of the context lines of a comment */
   public abstract ImmutableMap<Integer, String> lines();
 
+  /**
+   * Content type of the source file. Useful for syntax highlighting.
+   *
+   * @return text/x-gerrit-commit-message if the file is a commit message.
+   *     <p>text/x-gerrit-merge-list if the file is a merge list.
+   *     <p>The content/mime type, e.g. text/x-c++src otherwise.
+   */
+  public abstract String contentType();
+
   public static CommentContext empty() {
     return EMPTY;
   }
diff --git a/java/com/google/gerrit/entities/ImmutableConfig.java b/java/com/google/gerrit/entities/ImmutableConfig.java
new file mode 100644
index 0000000..a5efc14
--- /dev/null
+++ b/java/com/google/gerrit/entities/ImmutableConfig.java
@@ -0,0 +1,91 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.entities;
+
+import java.util.Set;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.Config;
+
+/**
+ * Immutable parsed representation of a {@link org.eclipse.jgit.lib.Config} that can be cached.
+ * Supports only a limited set of operations.
+ */
+public class ImmutableConfig {
+  public static final ImmutableConfig EMPTY = new ImmutableConfig("", new Config());
+
+  private final String stringCfg;
+  private final Config cfg;
+
+  private ImmutableConfig(String stringCfg, Config cfg) {
+    this.stringCfg = stringCfg;
+    this.cfg = cfg;
+  }
+
+  public static ImmutableConfig parse(String stringCfg) throws ConfigInvalidException {
+    Config cfg = new Config();
+    cfg.fromText(stringCfg);
+    return new ImmutableConfig(stringCfg, cfg);
+  }
+
+  /** Returns a mutable copy of this config. */
+  public Config mutableCopy() {
+    Config cfg = new Config();
+    try {
+      cfg.fromText(this.cfg.toText());
+    } catch (ConfigInvalidException e) {
+      // Can't happen as we used JGit to format that config.
+      throw new IllegalStateException(e);
+    }
+    return cfg;
+  }
+
+  /** @see Config#getSections() */
+  public Set<String> getSections() {
+    return cfg.getSections();
+  }
+
+  /** @see Config#getNames(String) */
+  public Set<String> getNames(String section) {
+    return cfg.getNames(section);
+  }
+
+  /** @see Config#getNames(String, String) */
+  public Set<String> getNames(String section, String subsection) {
+    return cfg.getNames(section, subsection);
+  }
+
+  /** @see Config#getStringList(String, String, String) */
+  public String[] getStringList(String section, String subsection, String name) {
+    return cfg.getStringList(section, subsection, name);
+  }
+
+  /** @see Config#getSubsections(String) */
+  public Set<String> getSubsections(String section) {
+    return cfg.getSubsections(section);
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof ImmutableConfig)) {
+      return false;
+    }
+    return ((ImmutableConfig) o).stringCfg.equals(stringCfg);
+  }
+
+  @Override
+  public int hashCode() {
+    return stringCfg.hashCode();
+  }
+}
diff --git a/java/com/google/gerrit/extensions/common/CommentInfo.java b/java/com/google/gerrit/extensions/common/CommentInfo.java
index fcce2b3..35587a0 100644
--- a/java/com/google/gerrit/extensions/common/CommentInfo.java
+++ b/java/com/google/gerrit/extensions/common/CommentInfo.java
@@ -30,6 +30,9 @@
    */
   public List<ContextLineInfo> contextLines;
 
+  /** Mime type of the underlying source file. Only available if context lines are requested. */
+  public String sourceContentType;
+
   @Override
   public boolean equals(Object o) {
     if (super.equals(o)) {
diff --git a/java/com/google/gerrit/extensions/common/GerritInfo.java b/java/com/google/gerrit/extensions/common/GerritInfo.java
index 2ae6703..3265a00 100644
--- a/java/com/google/gerrit/extensions/common/GerritInfo.java
+++ b/java/com/google/gerrit/extensions/common/GerritInfo.java
@@ -23,4 +23,5 @@
   public Boolean editGpgKeys;
   public String reportBugUrl;
   public String primaryWeblinkName;
+  public String instanceId;
 }
diff --git a/java/com/google/gerrit/server/ApprovalInference.java b/java/com/google/gerrit/server/ApprovalInference.java
index 572ae7a..d77427a 100644
--- a/java/com/google/gerrit/server/ApprovalInference.java
+++ b/java/com/google/gerrit/server/ApprovalInference.java
@@ -25,6 +25,7 @@
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.entities.Account;
 import com.google.gerrit.entities.LabelType;
+import com.google.gerrit.entities.LabelTypes;
 import com.google.gerrit.entities.Patch.ChangeType;
 import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
@@ -109,10 +110,10 @@
       PatchSetApproval psa,
       PatchSet.Id psId,
       ChangeKind kind,
-      PatchList patchList) {
+      LabelType type,
+      @Nullable PatchList patchList) {
     int n = psa.key().patchSetId().get();
     checkArgument(n != psId.get());
-    LabelType type = project.getLabelTypes().byLabel(psa.labelId());
 
     if (type == null) {
       logger.atFine().log(
@@ -367,12 +368,18 @@
     logger.atFine().log(
         "change kind for patch set %d of change %d against prior patch set %s is %s",
         ps.id().get(), ps.id().changeId().get(), priorPatchSet.getValue().id().changeId(), kind);
-    PatchList patchList = getPatchList(project, ps, priorPatchSet);
+    PatchList patchList = null;
+    LabelTypes labelTypes = project.getLabelTypes();
     for (PatchSetApproval psa : priorApprovals) {
       if (resultByUser.contains(psa.label(), psa.accountId())) {
         continue;
       }
-      if (!canCopy(project, psa, ps.id(), kind, patchList)) {
+      LabelType type = labelTypes.byLabel(psa.labelId());
+      // Only compute patchList if there is a relevant label, since this is expensive.
+      if (patchList == null && type != null && type.isCopyAllScoresIfListOfFilesDidNotChange()) {
+        patchList = getPatchList(project, ps, priorPatchSet);
+      }
+      if (!canCopy(project, psa, ps.id(), kind, type, patchList)) {
         continue;
       }
       resultByUser.put(psa.label(), psa.accountId(), psa.copyWithPatchSet(ps.id()));
diff --git a/java/com/google/gerrit/server/change/ReviewerJson.java b/java/com/google/gerrit/server/change/ReviewerJson.java
index a3136d4a..761b57d 100644
--- a/java/com/google/gerrit/server/change/ReviewerJson.java
+++ b/java/com/google/gerrit/server/change/ReviewerJson.java
@@ -32,7 +32,6 @@
 import com.google.gerrit.server.permissions.LabelPermission;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
-import com.google.gerrit.server.project.SubmitRuleEvaluator;
 import com.google.gerrit.server.project.SubmitRuleOptions;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.inject.Inject;
@@ -47,20 +46,17 @@
   private final ChangeData.Factory changeDataFactory;
   private final ApprovalsUtil approvalsUtil;
   private final AccountLoader.Factory accountLoaderFactory;
-  private final SubmitRuleEvaluator submitRuleEvaluator;
 
   @Inject
   ReviewerJson(
       PermissionBackend permissionBackend,
       ChangeData.Factory changeDataFactory,
       ApprovalsUtil approvalsUtil,
-      AccountLoader.Factory accountLoaderFactory,
-      SubmitRuleEvaluator.Factory submitRuleEvaluatorFactory) {
+      AccountLoader.Factory accountLoaderFactory) {
     this.permissionBackend = permissionBackend;
     this.changeDataFactory = changeDataFactory;
     this.approvalsUtil = approvalsUtil;
     this.accountLoaderFactory = accountLoaderFactory;
-    submitRuleEvaluator = submitRuleEvaluatorFactory.create(SubmitRuleOptions.defaults());
   }
 
   public List<ReviewerInfo> format(Collection<ReviewerResource> rsrcs)
@@ -123,7 +119,7 @@
     if (ps != null) {
       PermissionBackend.ForChange perm = permissionBackend.absentUser(reviewerAccountId).change(cd);
 
-      for (SubmitRecord rec : submitRuleEvaluator.evaluate(cd)) {
+      for (SubmitRecord rec : cd.submitRecords(SubmitRuleOptions.defaults())) {
         if (rec.labels == null) {
           continue;
         }
diff --git a/java/com/google/gerrit/server/comment/CommentContextCacheImpl.java b/java/com/google/gerrit/server/comment/CommentContextCacheImpl.java
index 3d75349..f44b075 100644
--- a/java/com/google/gerrit/server/comment/CommentContextCacheImpl.java
+++ b/java/com/google/gerrit/server/comment/CommentContextCacheImpl.java
@@ -68,7 +68,7 @@
       @Override
       protected void configure() {
         persist(CACHE_NAME, CommentContextKey.class, CommentContext.class)
-            .version(2)
+            .version(3)
             .diskLimit(1 << 30) // limit the total cache size to 1 GB
             .maximumWeight(1 << 23) // Limit the size of the in-memory cache to 8 MB
             .weigher(CommentContextWeigher.class)
@@ -149,6 +149,7 @@
     @Override
     public byte[] serialize(CommentContext commentContext) {
       AllCommentContextProto.Builder allBuilder = AllCommentContextProto.newBuilder();
+      allBuilder.setContentType(commentContext.contentType());
 
       commentContext
           .lines()
@@ -165,9 +166,10 @@
     @Override
     public CommentContext deserialize(byte[] in) {
       ImmutableMap.Builder<Integer, String> contextLinesMap = ImmutableMap.builder();
-      Protos.parseUnchecked(AllCommentContextProto.parser(), in).getContextList().stream()
+      AllCommentContextProto proto = Protos.parseUnchecked(AllCommentContextProto.parser(), in);
+      proto.getContextList().stream()
           .forEach(c -> contextLinesMap.put(c.getLineNumber(), c.getContextLine()));
-      return CommentContext.create(contextLinesMap.build());
+      return CommentContext.create(contextLinesMap.build(), proto.getContentType());
     }
   }
 
diff --git a/java/com/google/gerrit/server/comment/CommentContextLoader.java b/java/com/google/gerrit/server/comment/CommentContextLoader.java
index c93f4b1..4a6c956 100644
--- a/java/com/google/gerrit/server/comment/CommentContextLoader.java
+++ b/java/com/google/gerrit/server/comment/CommentContextLoader.java
@@ -16,6 +16,7 @@
 
 import static com.google.gerrit.entities.Patch.COMMIT_MSG;
 import static com.google.gerrit.entities.Patch.MERGE_LIST;
+import static com.google.gerrit.server.project.ProjectCache.illegalState;
 import static java.util.stream.Collectors.groupingBy;
 
 import com.google.auto.value.AutoValue;
@@ -23,15 +24,22 @@
 import com.google.common.collect.Iterables;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.common.Nullable;
+import com.google.gerrit.common.data.PatchScript;
 import com.google.gerrit.entities.Comment;
 import com.google.gerrit.entities.CommentContext;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.extensions.common.ContextLineInfo;
+import com.google.gerrit.server.change.FileContentUtil;
 import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.mime.FileTypeRegistry;
 import com.google.gerrit.server.patch.ComparisonType;
 import com.google.gerrit.server.patch.Text;
+import com.google.gerrit.server.project.ProjectCache;
+import com.google.gerrit.server.project.ProjectState;
 import com.google.inject.Inject;
 import com.google.inject.assistedinject.Assisted;
+import eu.medsea.mimeutil.MimeType;
+import eu.medsea.mimeutil.MimeUtil2;
 import java.io.IOException;
 import java.util.Collection;
 import java.util.List;
@@ -52,17 +60,25 @@
 public class CommentContextLoader {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
+  private final FileTypeRegistry registry;
   private final GitRepositoryManager repoManager;
   private final Project.NameKey project;
+  private final ProjectState projectState;
 
   public interface Factory {
     CommentContextLoader create(Project.NameKey project);
   }
 
   @Inject
-  CommentContextLoader(GitRepositoryManager repoManager, @Assisted Project.NameKey project) {
+  CommentContextLoader(
+      FileTypeRegistry registry,
+      GitRepositoryManager repoManager,
+      ProjectCache projectCache,
+      @Assisted Project.NameKey project) {
+    this.registry = registry;
     this.repoManager = repoManager;
     this.project = project;
+    projectState = projectCache.get(project).orElseThrow(illegalState(project));
   }
 
   /**
@@ -122,7 +138,8 @@
       ObjectReader reader, RevCommit commit, Range commentRange, int contextPadding)
       throws IOException {
     Text text = Text.forCommit(reader, commit);
-    return createContext(text, commentRange, contextPadding);
+    return createContext(
+        text, commentRange, contextPadding, FileContentUtil.TEXT_X_GERRIT_COMMIT_MESSAGE);
   }
 
   private CommentContext getContextForMergeList(
@@ -130,7 +147,8 @@
       throws IOException {
     ComparisonType cmp = ComparisonType.againstParent(1);
     Text text = Text.forMergeList(cmp, reader, commit);
-    return createContext(text, commentRange, contextPadding);
+    return createContext(
+        text, commentRange, contextPadding, FileContentUtil.TEXT_X_GERRIT_MERGE_LIST);
   }
 
   private CommentContext getContextForFilePath(
@@ -151,11 +169,23 @@
       }
       ObjectId id = tw.getObjectId(0);
       Text src = new Text(repo.open(id, Constants.OBJ_BLOB));
-      return createContext(src, commentRange, contextPadding);
+      String contentType = getContentType(tw, filePath, src);
+      return createContext(src, commentRange, contextPadding, contentType);
     }
   }
 
-  private static CommentContext createContext(Text src, Range commentRange, int contextPadding) {
+  private String getContentType(TreeWalk tw, String filePath, Text src) {
+    PatchScript.FileMode fileMode = PatchScript.FileMode.fromJgitFileMode(tw.getFileMode(0));
+    String mimeType = MimeUtil2.UNKNOWN_MIME_TYPE.toString();
+    if (src.size() > 0 && PatchScript.FileMode.SYMLINK != fileMode) {
+      MimeType registryMimeType = registry.getMimeType(filePath, src.getContent());
+      mimeType = registryMimeType.toString();
+    }
+    return FileContentUtil.resolveContentType(projectState, filePath, fileMode, mimeType);
+  }
+
+  private static CommentContext createContext(
+      Text src, Range commentRange, int contextPadding, String contentType) {
     if (commentRange.start() < 1 || commentRange.end() - 1 > src.size()) {
       // TODO(ghareeb): We should throw an exception in this case. See
       // https://bugs.chromium.org/p/gerrit/issues/detail?id=14102 which is an example where the
@@ -168,7 +198,7 @@
     for (int i = commentRange.start(); i < commentRange.end(); i++) {
       context.put(i, src.getString(i - 1));
     }
-    return CommentContext.create(context.build());
+    return CommentContext.create(context.build(), contentType);
   }
 
   /**
diff --git a/java/com/google/gerrit/server/git/validators/CommentCumulativeSizeValidator.java b/java/com/google/gerrit/server/git/validators/CommentCumulativeSizeValidator.java
index d507531..6e640f3 100644
--- a/java/com/google/gerrit/server/git/validators/CommentCumulativeSizeValidator.java
+++ b/java/com/google/gerrit/server/git/validators/CommentCumulativeSizeValidator.java
@@ -23,6 +23,7 @@
 import com.google.gerrit.extensions.validators.CommentValidationContext;
 import com.google.gerrit.extensions.validators.CommentValidationFailure;
 import com.google.gerrit.extensions.validators.CommentValidator;
+import com.google.gerrit.server.ChangeMessagesUtil;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.inject.Inject;
@@ -34,6 +35,8 @@
  * issues. Note that autogenerated change messages are not subject to validation.
  */
 public class CommentCumulativeSizeValidator implements CommentValidator {
+  public static final int DEFAULT_CUMULATIVE_COMMENT_SIZE_LIMIT = 3 << 20;
+
   private final int maxCumulativeSize;
   private final ChangeNotes.Factory notesFactory;
 
@@ -41,7 +44,9 @@
   CommentCumulativeSizeValidator(
       @GerritServerConfig Config serverConfig, ChangeNotes.Factory notesFactory) {
     this.notesFactory = notesFactory;
-    maxCumulativeSize = serverConfig.getInt("change", "cumulativeCommentSizeLimit", 3 << 20);
+    maxCumulativeSize =
+        serverConfig.getInt(
+            "change", "cumulativeCommentSizeLimit", DEFAULT_CUMULATIVE_COMMENT_SIZE_LIMIT);
   }
 
   @Override
@@ -55,7 +60,13 @@
                     notes.getRobotComments().values().stream())
                 .mapToInt(Comment::getApproximateSize)
                 .sum()
-            + notes.getChangeMessages().stream().mapToInt(cm -> cm.getMessage().length()).sum();
+            + notes.getChangeMessages().stream()
+                // Auto-generated change messages are not counted for the limit. This method is not
+                // called when those change messages are created, but we should also skip them when
+                // counting the size for unrelated messages.
+                .filter(cm -> !ChangeMessagesUtil.isAutogenerated(cm.getTag()))
+                .mapToInt(cm -> cm.getMessage().length())
+                .sum();
     int newCumulativeSize =
         comments.stream().mapToInt(CommentForValidation::getApproximateSize).sum();
     ImmutableList.Builder<CommentValidationFailure> failures = ImmutableList.builder();
diff --git a/java/com/google/gerrit/server/patch/AutoMerger.java b/java/com/google/gerrit/server/patch/AutoMerger.java
index fe915c5..ac37411 100644
--- a/java/com/google/gerrit/server/patch/AutoMerger.java
+++ b/java/com/google/gerrit/server/patch/AutoMerger.java
@@ -109,6 +109,7 @@
               ActionType.GIT_UPDATE,
               "createAutoMerge",
               () -> createAutoMergeCommit(repo, rw, ins, merge, mergeStrategy))
+          .defaultTimeoutMultiplier(2)
           .call();
     } catch (Exception e) {
       Throwables.throwIfUnchecked(e);
diff --git a/java/com/google/gerrit/server/patch/ComparisonType.java b/java/com/google/gerrit/server/patch/ComparisonType.java
index 260c507..eca2658 100644
--- a/java/com/google/gerrit/server/patch/ComparisonType.java
+++ b/java/com/google/gerrit/server/patch/ComparisonType.java
@@ -16,34 +16,40 @@
 
 import static com.google.gerrit.server.ioutil.BasicSerialization.readVarInt32;
 import static com.google.gerrit.server.ioutil.BasicSerialization.writeVarInt32;
-import static java.util.Objects.requireNonNull;
 
+import com.google.auto.value.AutoValue;
+import com.google.gerrit.server.cache.proto.Cache.FileDiffOutputProto;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.Optional;
 
-public class ComparisonType {
+/** Relation between the old and new commits used in the diff. */
+@AutoValue
+public abstract class ComparisonType {
 
-  /** 1-based parent */
-  private final Integer parentNum;
+  /**
+   * 1-based parent. Available if the old commit is the parent of the new commit and old commit is
+   * not the auto-merge.
+   */
+  abstract Optional<Integer> parentNum();
 
-  private final boolean autoMerge;
+  abstract boolean autoMerge();
 
   public static ComparisonType againstOtherPatchSet() {
-    return new ComparisonType(null, false);
+    return new AutoValue_ComparisonType(Optional.empty(), false);
   }
 
   public static ComparisonType againstParent(int parentNum) {
-    return new ComparisonType(parentNum, false);
+    return new AutoValue_ComparisonType(Optional.of(parentNum), false);
   }
 
   public static ComparisonType againstAutoMerge() {
-    return new ComparisonType(null, true);
+    return new AutoValue_ComparisonType(Optional.empty(), true);
   }
 
-  private ComparisonType(Integer parentNum, boolean autoMerge) {
-    this.parentNum = parentNum;
-    this.autoMerge = autoMerge;
+  private static ComparisonType create(Optional<Integer> parent, boolean automerge) {
+    return new AutoValue_ComparisonType(parent, automerge);
   }
 
   public boolean isAgainstParentOrAutoMerge() {
@@ -51,27 +57,43 @@
   }
 
   public boolean isAgainstParent() {
-    return parentNum != null;
+    return parentNum().isPresent();
   }
 
   public boolean isAgainstAutoMerge() {
-    return autoMerge;
+    return autoMerge();
   }
 
-  public int getParentNum() {
-    requireNonNull(parentNum);
-    return parentNum;
+  public Optional<Integer> getParentNum() {
+    return parentNum();
   }
 
   void writeTo(OutputStream out) throws IOException {
-    writeVarInt32(out, parentNum != null ? parentNum : 0);
-    writeVarInt32(out, autoMerge ? 1 : 0);
+    writeVarInt32(out, isAgainstParent() ? parentNum().get() : 0);
+    writeVarInt32(out, autoMerge() ? 1 : 0);
   }
 
   static ComparisonType readFrom(InputStream in) throws IOException {
     int p = readVarInt32(in);
-    Integer parentNum = p > 0 ? p : null;
+    Optional<Integer> parentNum = p > 0 ? Optional.of(p) : Optional.empty();
     boolean autoMerge = readVarInt32(in) != 0;
-    return new ComparisonType(parentNum, autoMerge);
+    return create(parentNum, autoMerge);
+  }
+
+  public FileDiffOutputProto.ComparisonType toProto() {
+    FileDiffOutputProto.ComparisonType.Builder builder =
+        FileDiffOutputProto.ComparisonType.newBuilder().setAutoMerge(autoMerge());
+    if (parentNum().isPresent()) {
+      builder.setParentNum(parentNum().get());
+    }
+    return builder.build();
+  }
+
+  public static ComparisonType fromProto(FileDiffOutputProto.ComparisonType proto) {
+    Optional<Integer> parentNum = Optional.empty();
+    if (proto.hasField(FileDiffOutputProto.ComparisonType.getDescriptor().findFieldByNumber(1))) {
+      parentNum = Optional.of(proto.getParentNum());
+    }
+    return create(parentNum, proto.getAutoMerge());
   }
 }
diff --git a/java/com/google/gerrit/server/patch/DiffOperations.java b/java/com/google/gerrit/server/patch/DiffOperations.java
index 8b90531..93aefff 100644
--- a/java/com/google/gerrit/server/patch/DiffOperations.java
+++ b/java/com/google/gerrit/server/patch/DiffOperations.java
@@ -74,8 +74,9 @@
   /**
    * Returns the diff for a single file between a patchset commit against its parent or the
    * auto-merge commit. For deleted files, the {@code fileName} parameter should contain the old
-   * name of the file. This method will return {@link FileDiffOutput#empty(String)} if the requested
-   * file identified by {@code fileName} has unchanged content or does not exist at both commits.
+   * name of the file. This method will return {@link FileDiffOutput#empty(String, ObjectId,
+   * ObjectId)} if the requested file identified by {@code fileName} has unchanged content or does
+   * not exist at both commits.
    *
    * @param project a project name representing a git repository.
    * @param newCommit 20 bytes SHA-1 of the new commit used in the diff.
@@ -98,8 +99,8 @@
   /**
    * Returns the diff for a single file between two patchset commits. For deleted files, the {@code
    * fileName} parameter should contain the old name of the file. This method will return {@link
-   * FileDiffOutput#empty(String)} if the requested file identified by {@code fileName} has
-   * unchanged content or does not exist at both commits.
+   * FileDiffOutput#empty(String, ObjectId, ObjectId)} if the requested file identified by {@code
+   * fileName} has unchanged content or does not exist at both commits.
    *
    * @param project a project name representing a git repository.
    * @param oldCommit 20 bytes SHA-1 of the old commit used in the diff.
diff --git a/java/com/google/gerrit/server/patch/DiffOperationsImpl.java b/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
index 16bd135..efb64bc 100644
--- a/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
+++ b/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
@@ -125,7 +125,9 @@
       FileDiffCacheKey key =
           createFileDiffCacheKey(project, diffParams.baseCommit(), newCommit, fileName, whitespace);
       Map<String, FileDiffOutput> result = getModifiedFilesForKeys(ImmutableList.of(key));
-      return result.containsKey(fileName) ? result.get(fileName) : FileDiffOutput.empty(fileName);
+      return result.containsKey(fileName)
+          ? result.get(fileName)
+          : FileDiffOutput.empty(fileName, key.oldCommit(), key.newCommit());
     } catch (IOException e) {
       throw new DiffNotAvailableException(
           "Failed to evaluate the parent/base commit for commit " + newCommit, e);
@@ -143,7 +145,9 @@
     FileDiffCacheKey key =
         createFileDiffCacheKey(project, oldCommit, newCommit, fileName, whitespace);
     Map<String, FileDiffOutput> result = getModifiedFilesForKeys(ImmutableList.of(key));
-    return result.containsKey(fileName) ? result.get(fileName) : FileDiffOutput.empty(fileName);
+    return result.containsKey(fileName)
+        ? result.get(fileName)
+        : FileDiffOutput.empty(fileName, oldCommit, newCommit);
   }
 
   private Map<String, FileDiffOutput> getModifiedFiles(
diff --git a/java/com/google/gerrit/server/patch/MagicFile.java b/java/com/google/gerrit/server/patch/MagicFile.java
index aa6b11f..e42dd8c 100644
--- a/java/com/google/gerrit/server/patch/MagicFile.java
+++ b/java/com/google/gerrit/server/patch/MagicFile.java
@@ -93,7 +93,7 @@
           }
         default:
           int uninterestingParent =
-              comparisonType.isAgainstParent() ? comparisonType.getParentNum() : 1;
+              comparisonType.isAgainstParent() ? comparisonType.getParentNum().get() : 1;
 
           b.append("Merge List:\n\n");
           for (RevCommit commit : MergeListBuilder.build(rw, c, uninterestingParent)) {
diff --git a/java/com/google/gerrit/server/patch/PatchScriptBuilder.java b/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
index c6f7acf..ae30113 100644
--- a/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
+++ b/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
@@ -405,12 +405,7 @@
       if (mode == FileMode.MISSING) {
         displayMethod = DisplayMethod.NONE;
       }
-      PatchScript.FileMode fileMode = PatchScript.FileMode.FILE;
-      if (mode == FileMode.SYMLINK) {
-        fileMode = PatchScript.FileMode.SYMLINK;
-      } else if (mode == FileMode.GITLINK) {
-        fileMode = PatchScript.FileMode.GITLINK;
-      }
+      PatchScript.FileMode fileMode = PatchScript.FileMode.fromJgitFileMode(mode);
       return new PatchSide(
           treeId, path, id, mode, srcContent, src, mimeType, displayMethod, fileMode);
     }
diff --git a/java/com/google/gerrit/server/patch/SubmitWithStickyApprovalDiff.java b/java/com/google/gerrit/server/patch/SubmitWithStickyApprovalDiff.java
index 9f58aaf..18d532b 100644
--- a/java/com/google/gerrit/server/patch/SubmitWithStickyApprovalDiff.java
+++ b/java/com/google/gerrit/server/patch/SubmitWithStickyApprovalDiff.java
@@ -30,7 +30,9 @@
 import com.google.gerrit.prettify.common.SparseFileContent;
 import com.google.gerrit.prettify.common.SparseFileContent.Accessor;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.git.LargeObjectException;
+import com.google.gerrit.server.git.validators.CommentCumulativeSizeValidator;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.gerrit.server.project.InvalidChangeOperationException;
@@ -41,6 +43,7 @@
 import java.util.List;
 import java.util.stream.Collectors;
 import org.eclipse.jgit.diff.Edit;
+import org.eclipse.jgit.lib.Config;
 
 /**
  * This class is used on submit to compute the diff between the latest approved patch-set, and the
@@ -58,15 +61,22 @@
   private final ProjectCache projectCache;
   private final PatchScriptFactory.Factory patchScriptFactoryFactory;
   private final PatchListCache patchListCache;
+  private final int maxCumulativeSize;
 
   @Inject
   SubmitWithStickyApprovalDiff(
       ProjectCache projectCache,
       PatchScriptFactory.Factory patchScriptFactoryFactory,
-      PatchListCache patchListCache) {
+      PatchListCache patchListCache,
+      @GerritServerConfig Config serverConfig) {
     this.projectCache = projectCache;
     this.patchScriptFactoryFactory = patchScriptFactoryFactory;
     this.patchListCache = patchListCache;
+    maxCumulativeSize =
+        serverConfig.getInt(
+            "change",
+            "cumulativeCommentSizeLimit",
+            CommentCumulativeSizeValidator.DEFAULT_CUMULATIVE_COMMENT_SIZE_LIMIT);
   }
 
   public String apply(ChangeNotes notes, CurrentUser currentUser)
@@ -88,8 +98,10 @@
       // If the latest approved patchset is the current patchset, no need to return anything.
       return "";
     }
-    String diff =
-        String.format("\n\n%d is the latest approved patch-set.\n", latestApprovedPatchsetId.get());
+    StringBuilder diff =
+        new StringBuilder(
+            String.format(
+                "\n\n%d is the latest approved patch-set.\n", latestApprovedPatchsetId.get()));
     PatchList patchList =
         getPatchList(
             notes.getProjectName(),
@@ -103,19 +115,29 @@
             .collect(Collectors.toList());
 
     if (patchListEntryList.isEmpty()) {
-      diff +=
-          "No files were changed between the latest approved patch-set and the submitted one.\n";
-      return diff;
+      diff.append(
+          "No files were changed between the latest approved patch-set and the submitted one.\n");
+      return diff.toString();
     }
 
-    diff += "The change was submitted with unreviewed changes in the following files:\n\n";
+    diff.append("The change was submitted with unreviewed changes in the following files:\n\n");
 
     for (PatchListEntry patchListEntry : patchListEntryList) {
-      diff +=
+      diff.append(
           getDiffForFile(
-              notes, currentPatchset.id(), latestApprovedPatchsetId, patchListEntry, currentUser);
+              notes, currentPatchset.id(), latestApprovedPatchsetId, patchListEntry, currentUser));
     }
-    return diff;
+    if (diff.length() > maxCumulativeSize) {
+      // The diff length is not counted as part of the limit (for technical reasons, since we'd
+      // have to call CommentCumulativeSizeValidator), but it's best not to post an extra large
+      // change message here.
+      return String.format(
+          "\n\n%d is the latest approved patch-set.\nThe change was submitted "
+              + "with many unreviewed changes (the diff is too large to show). Please review the "
+              + "diff.",
+          latestApprovedPatchsetId.get());
+    }
+    return diff.toString();
   }
 
   private String getDiffForFile(
@@ -126,12 +148,13 @@
       CurrentUser currentUser)
       throws AuthException, InvalidChangeOperationException, IOException,
           PermissionBackendException {
-    String diff =
-        String.format(
-            "The name of the file: %s\nInsertions: %d, Deletions: %d.\n\n",
-            patchListEntry.getNewName(),
-            patchListEntry.getInsertions(),
-            patchListEntry.getDeletions());
+    StringBuilder diff =
+        new StringBuilder(
+            String.format(
+                "The name of the file: %s\nInsertions: %d, Deletions: %d.\n\n",
+                patchListEntry.getNewName(),
+                patchListEntry.getInsertions(),
+                patchListEntry.getDeletions()));
     DiffPreferencesInfo diffPreferencesInfo = createDefaultDiffPreferencesInfo();
     PatchScriptFactory patchScriptFactory =
         patchScriptFactoryFactory.create(
@@ -145,66 +168,66 @@
     try {
       patchScript = patchScriptFactory.call();
     } catch (LargeObjectException exception) {
-      diff += "The file content is too large for showing the full diff. \n\n";
-      return diff;
+      diff.append("The file content is too large for showing the full diff. \n\n");
+      return diff.toString();
     }
     if (patchScript.getChangeType() == ChangeType.RENAMED) {
-      diff +=
+      diff.append(
           String.format(
               "The file %s was renamed to %s\n",
-              patchListEntry.getOldName(), patchListEntry.getNewName());
+              patchListEntry.getOldName(), patchListEntry.getNewName()));
     }
     SparseFileContent.Accessor fileA = patchScript.getA().createAccessor();
     SparseFileContent.Accessor fileB = patchScript.getB().createAccessor();
     boolean editsExist = false;
     if (patchScript.getEdits().stream().anyMatch(e -> e.getType() != Edit.Type.EMPTY)) {
-      diff += "```\n";
+      diff.append("```\n");
       editsExist = true;
     }
     for (Edit edit : patchScript.getEdits()) {
-      diff += getDiffForEdit(fileA, fileB, edit);
+      diff.append(getDiffForEdit(fileA, fileB, edit));
     }
     if (editsExist) {
-      diff += "```\n";
+      diff.append("```\n");
     }
-    return diff;
+    return diff.toString();
   }
 
   private String getDiffForEdit(Accessor fileA, Accessor fileB, Edit edit) {
-    String diff = "";
+    StringBuilder diff = new StringBuilder();
     Edit.Type type = edit.getType();
     switch (type) {
       case INSERT:
-        diff += String.format("@@ +%d:%d @@\n", edit.getBeginB(), edit.getEndB());
-        diff += getModifiedLines(fileB, edit.getBeginB(), edit.getEndB(), '+');
-        diff += "\n";
+        diff.append(String.format("@@ +%d:%d @@\n", edit.getBeginB(), edit.getEndB()));
+        diff.append(getModifiedLines(fileB, edit.getBeginB(), edit.getEndB(), '+'));
+        diff.append("\n");
         break;
       case DELETE:
-        diff += String.format("@@ -%d:%d @@\n", edit.getBeginA(), edit.getEndA());
-        diff += getModifiedLines(fileA, edit.getBeginA(), edit.getEndA(), '-');
-        diff += "\n";
+        diff.append(String.format("@@ -%d:%d @@\n", edit.getBeginA(), edit.getEndA()));
+        diff.append(getModifiedLines(fileA, edit.getBeginA(), edit.getEndA(), '-'));
+        diff.append("\n");
         break;
       case REPLACE:
-        diff +=
+        diff.append(
             String.format(
                 "@@ -%d:%d, +%d:%d @@\n",
-                edit.getBeginA(), edit.getEndA(), edit.getBeginB(), edit.getEndB());
-        diff += getModifiedLines(fileA, edit.getBeginA(), edit.getEndA(), '-');
-        diff += getModifiedLines(fileB, edit.getBeginB(), edit.getEndB(), '+');
-        diff += "\n";
+                edit.getBeginA(), edit.getEndA(), edit.getBeginB(), edit.getEndB()));
+        diff.append(getModifiedLines(fileA, edit.getBeginA(), edit.getEndA(), '-'));
+        diff.append(getModifiedLines(fileB, edit.getBeginB(), edit.getEndB(), '+'));
+        diff.append("\n");
         break;
       case EMPTY:
         // do nothing since there is no change here.
     }
-    return diff;
+    return diff.toString();
   }
 
   private String getModifiedLines(Accessor file, int begin, int end, char modificationType) {
-    String diff = "";
+    StringBuilder diff = new StringBuilder();
     for (int i = begin; i < end; i++) {
-      diff += String.format("%c  %s\n", modificationType, file.get(i));
+      diff.append(String.format("%c  %s\n", modificationType, file.get(i)));
     }
-    return diff;
+    return diff.toString();
   }
 
   private DiffPreferencesInfo createDefaultDiffPreferencesInfo() {
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
index 63f311b..1bb407d 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
@@ -93,6 +93,7 @@
         persist(DIFF, FileDiffCacheKey.class, FileDiffOutput.class)
             .maximumWeight(10 << 20)
             .weigher(FileDiffWeigher.class)
+            .version(2)
             .keySerializer(FileDiffCacheKey.Serializer.INSTANCE)
             .valueSerializer(FileDiffOutput.Serializer.INSTANCE)
             .loader(FileDiffLoader.class);
@@ -219,19 +220,16 @@
         RawTextComparator cmp = comparatorFor(key.whitespace());
         ComparisonType comparisonType =
             getComparisonType(rw, reader, key.oldCommit(), key.newCommit());
-        RevCommit aCommit =
-            comparisonType.isAgainstParentOrAutoMerge()
-                ? null
-                : DiffUtil.getRevCommit(rw, key.oldCommit());
+        RevCommit aCommit = DiffUtil.getRevCommit(rw, key.oldCommit());
         RevCommit bCommit = DiffUtil.getRevCommit(rw, key.newCommit());
         return magicPath == MagicPath.COMMIT
-            ? createCommitEntry(reader, aCommit, bCommit, cmp, key.diffAlgorithm())
+            ? createCommitEntry(reader, aCommit, bCommit, comparisonType, cmp, key.diffAlgorithm())
             : createMergeListEntry(
                 reader, aCommit, bCommit, comparisonType, cmp, key.diffAlgorithm());
       } catch (IOException e) {
         logger.atWarning().log("Failed to compute commit entry for key %s", key);
       }
-      return FileDiffOutput.empty(key.newFilePath());
+      return FileDiffOutput.empty(key.newFilePath(), key.oldCommit(), key.newCommit());
     }
 
     private static RawTextComparator comparatorFor(Whitespace ws) {
@@ -255,13 +253,24 @@
         ObjectReader reader,
         RevCommit oldCommit,
         RevCommit newCommit,
+        ComparisonType comparisonType,
         RawTextComparator rawTextComparator,
         GitFileDiffCacheImpl.DiffAlgorithm diffAlgorithm)
         throws IOException {
-      Text aText = oldCommit != null ? Text.forCommit(reader, oldCommit) : Text.EMPTY;
+      Text aText =
+          comparisonType.isAgainstParentOrAutoMerge()
+              ? Text.EMPTY
+              : Text.forCommit(reader, oldCommit);
       Text bText = Text.forCommit(reader, newCommit);
       return createMagicFileDiffOutput(
-          rawTextComparator, oldCommit, aText, bText, Patch.COMMIT_MSG, diffAlgorithm);
+          oldCommit,
+          newCommit,
+          comparisonType,
+          rawTextComparator,
+          aText,
+          bText,
+          Patch.COMMIT_MSG,
+          diffAlgorithm);
     }
 
     private FileDiffOutput createMergeListEntry(
@@ -273,20 +282,31 @@
         GitFileDiffCacheImpl.DiffAlgorithm diffAlgorithm)
         throws IOException {
       Text aText =
-          oldCommit != null ? Text.forMergeList(comparisonType, reader, oldCommit) : Text.EMPTY;
+          comparisonType.isAgainstParentOrAutoMerge()
+              ? Text.EMPTY
+              : Text.forMergeList(comparisonType, reader, oldCommit);
       Text bText = Text.forMergeList(comparisonType, reader, newCommit);
       return createMagicFileDiffOutput(
-          rawTextComparator, oldCommit, aText, bText, Patch.MERGE_LIST, diffAlgorithm);
+          oldCommit,
+          newCommit,
+          comparisonType,
+          rawTextComparator,
+          aText,
+          bText,
+          Patch.MERGE_LIST,
+          diffAlgorithm);
     }
 
     private static FileDiffOutput createMagicFileDiffOutput(
+        ObjectId oldCommit,
+        ObjectId newCommit,
+        ComparisonType comparisonType,
         RawTextComparator rawTextComparator,
-        RevCommit aCommit,
         Text aText,
         Text bText,
         String fileName,
         GitFileDiffCacheImpl.DiffAlgorithm diffAlgorithm) {
-      byte[] rawHdr = getRawHeader(aCommit != null, fileName);
+      byte[] rawHdr = getRawHeader(!comparisonType.isAgainstParentOrAutoMerge(), fileName);
       byte[] aContent = aText.getContent();
       byte[] bContent = bText.getContent();
       long size = bContent.length;
@@ -298,6 +318,9 @@
       FileHeader fileHeader = new FileHeader(rawHdr, edits, PatchType.UNIFIED);
       Patch.ChangeType changeType = FileHeaderUtil.getChangeType(fileHeader);
       return FileDiffOutput.builder()
+          .oldCommitId(oldCommit)
+          .newCommitId(newCommit)
+          .comparisonType(comparisonType)
           .oldPath(FileHeaderUtil.getOldPath(fileHeader))
           .newPath(FileHeaderUtil.getNewPath(fileHeader))
           .changeType(changeType)
@@ -370,8 +393,13 @@
                         mainGitDiff.newPath().get())
                 : 0;
 
+        ObjectId oldCommit = augmentedKey.key().oldCommit();
+        ObjectId newCommit = augmentedKey.key().newCommit();
         FileDiffOutput fileDiff =
             FileDiffOutput.builder()
+                .oldCommitId(oldCommit)
+                .newCommitId(newCommit)
+                .comparisonType(getComparisonType(rw, reader, oldCommit, newCommit))
                 .changeType(mainGitDiff.changeType())
                 .patchType(mainGitDiff.patchType())
                 .oldPath(mainGitDiff.oldPath())
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java b/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
index 3348033..e7f47ef 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffOutput.java
@@ -24,16 +24,28 @@
 import com.google.gerrit.proto.Protos;
 import com.google.gerrit.server.cache.proto.Cache.FileDiffOutputProto;
 import com.google.gerrit.server.cache.serialize.CacheSerializer;
+import com.google.gerrit.server.cache.serialize.ObjectIdConverter;
+import com.google.gerrit.server.patch.ComparisonType;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import java.io.Serializable;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import org.eclipse.jgit.lib.ObjectId;
 
 /** File diff for a single file path. Produced as output of the {@link FileDiffCache}. */
 @AutoValue
 public abstract class FileDiffOutput implements Serializable {
   private static final long serialVersionUID = 1L;
 
+  /** The 20 bytes SHA-1 object ID of the old git commit used in the diff. */
+  public abstract ObjectId oldCommitId();
+
+  /** The 20 bytes SHA-1 object ID of the new git commit used in the diff. */
+  public abstract ObjectId newCommitId();
+
+  /** Comparison type of old and new commits: against another patchset, parent or auto-merge. */
+  public abstract ComparisonType comparisonType();
+
   /**
    * The file path at the old commit. Returns an empty Optional if {@link #changeType()} is equal to
    * {@link ChangeType#ADDED}.
@@ -95,8 +107,11 @@
   }
 
   /** Returns an entity representing an unchanged file between two commits. */
-  public static FileDiffOutput empty(String filePath) {
+  public static FileDiffOutput empty(String filePath, ObjectId oldCommitId, ObjectId newCommitId) {
     return builder()
+        .oldCommitId(oldCommitId)
+        .newCommitId(newCommitId)
+        .comparisonType(ComparisonType.againstOtherPatchSet()) // not important
         .oldPath(Optional.empty())
         .newPath(Optional.of(filePath))
         .changeType(ChangeType.MODIFIED)
@@ -124,6 +139,8 @@
     if (newPath().isPresent()) {
       result += stringSize(newPath().get());
     }
+    result += 20 + 20; // old and new commit IDs
+    result += 4; // comparison type
     result += 4; // changeType
     if (patchType().isPresent()) {
       result += 4;
@@ -140,6 +157,12 @@
   @AutoValue.Builder
   public abstract static class Builder {
 
+    public abstract Builder oldCommitId(ObjectId value);
+
+    public abstract Builder newCommitId(ObjectId value);
+
+    public abstract Builder comparisonType(ComparisonType value);
+
     public abstract Builder oldPath(Optional<String> value);
 
     public abstract Builder newPath(Optional<String> value);
@@ -173,8 +196,12 @@
 
     @Override
     public byte[] serialize(FileDiffOutput fileDiff) {
+      ObjectIdConverter idConverter = ObjectIdConverter.create();
       FileDiffOutputProto.Builder builder =
           FileDiffOutputProto.newBuilder()
+              .setOldCommit(idConverter.toByteString(fileDiff.oldCommitId().toObjectId()))
+              .setNewCommit(idConverter.toByteString(fileDiff.newCommitId().toObjectId()))
+              .setComparisonType(fileDiff.comparisonType().toProto())
               .setSize(fileDiff.size())
               .setSizeDelta(fileDiff.sizeDelta())
               .addAllHeaderLines(fileDiff.headerLines())
@@ -212,9 +239,13 @@
 
     @Override
     public FileDiffOutput deserialize(byte[] in) {
+      ObjectIdConverter idConverter = ObjectIdConverter.create();
       FileDiffOutputProto proto = Protos.parseUnchecked(FileDiffOutputProto.parser(), in);
       FileDiffOutput.Builder builder = FileDiffOutput.builder();
       builder
+          .oldCommitId(idConverter.fromByteString(proto.getOldCommit()))
+          .newCommitId(idConverter.fromByteString(proto.getNewCommit()))
+          .comparisonType(ComparisonType.fromProto(proto.getComparisonType()))
           .size(proto.getSize())
           .sizeDelta(proto.getSizeDelta())
           .headerLines(proto.getHeaderLinesList().stream().collect(ImmutableList.toImmutableList()))
diff --git a/java/com/google/gerrit/server/project/ProjectLevelConfig.java b/java/com/google/gerrit/server/project/ProjectLevelConfig.java
index 4825233..d82a318 100644
--- a/java/com/google/gerrit/server/project/ProjectLevelConfig.java
+++ b/java/com/google/gerrit/server/project/ProjectLevelConfig.java
@@ -16,14 +16,15 @@
 
 import static java.util.stream.Collectors.toList;
 
-import com.google.common.collect.Iterables;
 import com.google.common.collect.Streams;
+import com.google.gerrit.entities.ImmutableConfig;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.server.git.meta.VersionedMetaData;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Set;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.lib.CommitBuilder;
@@ -73,19 +74,17 @@
 
   private final String fileName;
   private final ProjectState project;
-  private Config cfg;
+  private final ImmutableConfig immutableConfig;
 
-  public ProjectLevelConfig(String fileName, ProjectState project, Config cfg) {
+  public ProjectLevelConfig(
+      String fileName, ProjectState project, @Nullable ImmutableConfig immutableConfig) {
     this.fileName = fileName;
     this.project = project;
-    this.cfg = cfg;
+    this.immutableConfig = immutableConfig == null ? ImmutableConfig.EMPTY : immutableConfig;
   }
 
   public Config get() {
-    if (cfg == null) {
-      cfg = new Config();
-    }
-    return cfg;
+    return immutableConfig.mutableCopy();
   }
 
   public Config getWithInheritance() {
@@ -105,58 +104,61 @@
    * @return a combined config.
    */
   public Config getWithInheritance(boolean merge) {
-    Config cfgWithInheritance = new Config();
-    try {
-      cfgWithInheritance.fromText(get().toText());
-    } catch (ConfigInvalidException e) {
-      // cannot happen
-    }
-    ProjectState parent = Iterables.getFirst(project.parents(), null);
-    if (parent != null) {
-      Config parentCfg = parent.getConfig(fileName).getWithInheritance();
-      for (String section : parentCfg.getSections()) {
-        Set<String> allNames = get().getNames(section);
-        for (String name : parentCfg.getNames(section)) {
-          String[] parentValues = parentCfg.getStringList(section, null, name);
-          if (!allNames.contains(name)) {
-            cfgWithInheritance.setStringList(section, null, name, Arrays.asList(parentValues));
-          } else if (merge) {
-            cfgWithInheritance.setStringList(
-                section,
-                null,
-                name,
-                Stream.concat(
-                        Arrays.stream(cfg.getStringList(section, null, name)),
-                        Arrays.stream(parentValues))
-                    .sorted()
-                    .distinct()
-                    .collect(toList()));
-          }
-        }
+    Config cfg = new Config();
+    // Traverse from All-Projects down to the current project
+    StreamSupport.stream(project.treeInOrder().spliterator(), false)
+        .forEach(
+            parent -> {
+              ImmutableConfig levelCfg = parent.getConfig(fileName).immutableConfig;
+              for (String section : levelCfg.getSections()) {
+                Set<String> allNames = cfg.getNames(section);
+                for (String name : levelCfg.getNames(section)) {
+                  String[] levelValues = levelCfg.getStringList(section, null, name);
+                  if (allNames.contains(name) && merge) {
+                    cfg.setStringList(
+                        section,
+                        null,
+                        name,
+                        Stream.concat(
+                                Arrays.stream(cfg.getStringList(section, null, name)),
+                                Arrays.stream(levelValues))
+                            .sorted()
+                            .distinct()
+                            .collect(toList()));
+                  } else {
+                    cfg.setStringList(section, null, name, Arrays.asList(levelValues));
+                  }
+                }
 
-        for (String subsection : parentCfg.getSubsections(section)) {
-          allNames = get().getNames(section, subsection);
-          for (String name : parentCfg.getNames(section, subsection)) {
-            String[] parentValues = parentCfg.getStringList(section, subsection, name);
-            if (!allNames.contains(name)) {
-              cfgWithInheritance.setStringList(
-                  section, subsection, name, Arrays.asList(parentValues));
-            } else if (merge) {
-              cfgWithInheritance.setStringList(
-                  section,
-                  subsection,
-                  name,
-                  Streams.concat(
-                          Arrays.stream(cfg.getStringList(section, subsection, name)),
-                          Arrays.stream(parentValues))
-                      .sorted()
-                      .distinct()
-                      .collect(toList()));
-            }
-          }
-        }
-      }
-    }
-    return cfgWithInheritance;
+                for (String subsection : levelCfg.getSubsections(section)) {
+                  allNames = cfg.getNames(section, subsection);
+
+                  Set<String> allNamesLevelCfg = levelCfg.getNames(section, subsection);
+                  if (allNamesLevelCfg.isEmpty()) {
+                    // Set empty subsection.
+                    cfg.setString(section, subsection, null, null);
+                  } else {
+                    for (String name : allNamesLevelCfg) {
+                      String[] levelValues = levelCfg.getStringList(section, subsection, name);
+                      if (allNames.contains(name) && merge) {
+                        cfg.setStringList(
+                            section,
+                            subsection,
+                            name,
+                            Streams.concat(
+                                    Arrays.stream(cfg.getStringList(section, subsection, name)),
+                                    Arrays.stream(levelValues))
+                                .sorted()
+                                .distinct()
+                                .collect(toList()));
+                      } else {
+                        cfg.setStringList(section, subsection, name, Arrays.asList(levelValues));
+                      }
+                    }
+                  }
+                }
+              }
+            });
+    return cfg;
   }
 }
diff --git a/java/com/google/gerrit/server/project/ProjectState.java b/java/com/google/gerrit/server/project/ProjectState.java
index 8c024ef..249eb35 100644
--- a/java/com/google/gerrit/server/project/ProjectState.java
+++ b/java/com/google/gerrit/server/project/ProjectState.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.project;
 
+import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.gerrit.entities.PermissionRule.Action.ALLOW;
 import static java.util.Comparator.comparing;
@@ -176,8 +177,9 @@
   }
 
   public ProjectLevelConfig getConfig(String fileName) {
-    Optional<Config> rawConfig = cachedConfig.getProjectLevelConfig(fileName);
-    return new ProjectLevelConfig(fileName, this, rawConfig.orElse(new Config()));
+    checkState(fileName.endsWith(".config"), "file name must end in .config. is: " + fileName);
+    return new ProjectLevelConfig(
+        fileName, this, cachedConfig.getParsedProjectLevelConfigs().get(fileName));
   }
 
   public long getMaxObjectSizeLimit() {
diff --git a/java/com/google/gerrit/server/query/change/ChangeData.java b/java/com/google/gerrit/server/query/change/ChangeData.java
index f047543..bf56000 100644
--- a/java/com/google/gerrit/server/query/change/ChangeData.java
+++ b/java/com/google/gerrit/server/query/change/ChangeData.java
@@ -872,36 +872,25 @@
   }
 
   public List<SubmitRecord> submitRecords(SubmitRuleOptions options) {
-    List<SubmitRecord> records = getCachedSubmitRecord(options);
+    // If the change is not submitted yet, 'strict' and 'lenient' both have the same result. If the
+    // change is submitted, SubmitRecord requested with 'strict' will contain just a single entry
+    // that with status=CLOSED. The latter is cheap to evaluate as we don't have to run any actual
+    // evaluation.
+    List<SubmitRecord> records = submitRecords.get(options);
     if (records == null) {
       if (!lazyLoad) {
         return Collections.emptyList();
       }
       records = submitRuleEvaluatorFactory.create(options).evaluate(this);
       submitRecords.put(options, records);
+      if (!change().isClosed() && submitRecords.size() == 1) {
+        // Cache the SubmitRecord with allowClosed = !allowClosed as the SubmitRecord are the same.
+        submitRecords.put(options.toBuilder().allowClosed(!options.allowClosed()).build(), records);
+      }
     }
     return records;
   }
 
-  @Nullable
-  public List<SubmitRecord> getSubmitRecords(SubmitRuleOptions options) {
-    return getCachedSubmitRecord(options);
-  }
-
-  private List<SubmitRecord> getCachedSubmitRecord(SubmitRuleOptions options) {
-    List<SubmitRecord> records = submitRecords.get(options);
-    if (records != null) {
-      return records;
-    }
-
-    if (options.allowClosed() && change != null && change.getStatus().isOpen()) {
-      SubmitRuleOptions openSubmitRuleOptions = options.toBuilder().allowClosed(false).build();
-      return submitRecords.get(openSubmitRuleOptions);
-    }
-
-    return null;
-  }
-
   public void setSubmitRecords(SubmitRuleOptions options, List<SubmitRecord> records) {
     submitRecords.put(options, records);
   }
diff --git a/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java b/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
index 68a90d2..4e3edcd 100644
--- a/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
+++ b/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java
@@ -173,6 +173,7 @@
   public static final String FIELD_MESSAGE = "message";
   public static final String FIELD_OWNER = "owner";
   public static final String FIELD_OWNERIN = "ownerin";
+  public static final String FIELD_PARENTOF = "parentof";
   public static final String FIELD_PARENTPROJECT = "parentproject";
   public static final String FIELD_PATH = "path";
   public static final String FIELD_PENDING_REVIEWER = "pendingreviewer";
@@ -735,6 +736,16 @@
   }
 
   @Operator
+  public Predicate<ChangeData> parentof(String value) throws QueryParseException {
+    List<ChangeData> changes = parseChangeData(value);
+    List<Predicate<ChangeData>> or = new ArrayList<>(changes.size());
+    for (ChangeData c : changes) {
+      or.add(new ParentOfPredicate(value, c, args.repoManager));
+    }
+    return Predicate.or(or);
+  }
+
+  @Operator
   public Predicate<ChangeData> parentproject(String name) {
     return new ParentProjectPredicate(args.projectCache, args.childProjects, name);
   }
@@ -1560,14 +1571,18 @@
   }
 
   private List<Change> parseChange(String value) throws QueryParseException {
+    return asChanges(parseChangeData(value));
+  }
+
+  private List<ChangeData> parseChangeData(String value) throws QueryParseException {
     if (PAT_LEGACY_ID.matcher(value).matches()) {
       Optional<Change.Id> id = Change.Id.tryParse(value);
       if (!id.isPresent()) {
         throw error("Invalid change id " + value);
       }
-      return asChanges(args.queryProvider.get().byLegacyChangeId(id.get()));
+      return args.queryProvider.get().byLegacyChangeId(id.get());
     } else if (PAT_CHANGE_ID.matcher(value).matches()) {
-      List<Change> changes = asChanges(args.queryProvider.get().byKeyPrefix(parseChangeId(value)));
+      List<ChangeData> changes = args.queryProvider.get().byKeyPrefix(parseChangeId(value));
       if (changes.isEmpty()) {
         throw error("Change " + value + " not found");
       }
diff --git a/java/com/google/gerrit/server/query/change/ParentOfPredicate.java b/java/com/google/gerrit/server/query/change/ParentOfPredicate.java
new file mode 100644
index 0000000..e48d586
--- /dev/null
+++ b/java/com/google/gerrit/server/query/change/ParentOfPredicate.java
@@ -0,0 +1,62 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.query.change;
+
+import com.google.common.collect.Sets;
+import com.google.gerrit.entities.PatchSet;
+import com.google.gerrit.exceptions.StorageException;
+import com.google.gerrit.index.query.Matchable;
+import com.google.gerrit.index.query.OperatorPredicate;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import java.io.IOException;
+import java.util.Set;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+public class ParentOfPredicate extends OperatorPredicate<ChangeData>
+    implements Matchable<ChangeData> {
+  protected final Set<RevCommit> parents;
+
+  public ParentOfPredicate(String value, ChangeData change, GitRepositoryManager repoManager) {
+    super(ChangeQueryBuilder.FIELD_PARENTOF, value);
+    this.parents = getParents(change, repoManager);
+  }
+
+  @Override
+  public boolean match(ChangeData changeData) {
+    return changeData.patchSets().stream().anyMatch(ps -> parents.contains(ps.commitId()));
+  }
+
+  @Override
+  public int getCost() {
+    return 1;
+  }
+
+  protected Set<RevCommit> getParents(ChangeData change, GitRepositoryManager repoManager) {
+    PatchSet ps = change.currentPatchSet();
+    try (Repository repo = repoManager.openRepository(change.project());
+        RevWalk walk = new RevWalk(repo)) {
+      RevCommit c = walk.parseCommit(ps.commitId());
+      return Sets.newHashSet(c.getParents());
+    } catch (IOException e) {
+      throw new StorageException(
+          String.format(
+              "Loading commit %s for ps %d of change %d failed.",
+              ps.commitId(), ps.id().get(), ps.id().changeId().get()),
+          e);
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/restapi/change/CommentJson.java b/java/com/google/gerrit/server/restapi/change/CommentJson.java
index 77b58c6..edc8fcf 100644
--- a/java/com/google/gerrit/server/restapi/change/CommentJson.java
+++ b/java/com/google/gerrit/server/restapi/change/CommentJson.java
@@ -171,7 +171,10 @@
           allComments.stream().map(this::createCommentContextKey).collect(toList());
       ImmutableMap<CommentContextKey, CommentContext> allContext = commentContextCache.getAll(keys);
       for (T c : allComments) {
-        c.contextLines = toContextLineInfoList(allContext.get(createCommentContextKey(c)));
+        CommentContextKey contextKey = createCommentContextKey(c);
+        CommentContext commentContext = allContext.get(contextKey);
+        c.contextLines = toContextLineInfoList(commentContext);
+        c.sourceContentType = commentContext.contentType();
       }
     }
 
diff --git a/java/com/google/gerrit/server/restapi/change/PostReview.java b/java/com/google/gerrit/server/restapi/change/PostReview.java
index 562bdf8..73b38b2 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReview.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReview.java
@@ -1228,9 +1228,10 @@
     }
 
     private boolean isReviewer(ChangeContext ctx) {
-      ChangeData cd = changeDataFactory.create(ctx.getNotes());
-      ReviewerSet reviewers = cd.reviewers();
-      return reviewers.byState(REVIEWER).contains(ctx.getAccountId());
+      return approvalsUtil
+          .getReviewers(ctx.getNotes())
+          .byState(REVIEWER)
+          .contains(ctx.getAccountId());
     }
 
     private boolean updateLabels(ProjectState projectState, ChangeContext ctx)
diff --git a/java/com/google/gerrit/server/restapi/change/ReviewersUtil.java b/java/com/google/gerrit/server/restapi/change/ReviewersUtil.java
index 2a55e41..38be27e 100644
--- a/java/com/google/gerrit/server/restapi/change/ReviewersUtil.java
+++ b/java/com/google/gerrit/server/restapi/change/ReviewersUtil.java
@@ -51,6 +51,7 @@
 import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.account.GroupBackend;
 import com.google.gerrit.server.account.GroupMembers;
+import com.google.gerrit.server.account.ServiceUserClassifier;
 import com.google.gerrit.server.change.ReviewerAdder;
 import com.google.gerrit.server.index.account.AccountField;
 import com.google.gerrit.server.index.account.AccountIndexCollection;
@@ -130,6 +131,7 @@
   private final IndexConfig indexConfig;
   private final AccountControl.Factory accountControlFactory;
   private final Provider<CurrentUser> self;
+  private final ServiceUserClassifier serviceUserClassifier;
 
   @Inject
   ReviewersUtil(
@@ -143,7 +145,8 @@
       AccountIndexCollection accountIndexes,
       IndexConfig indexConfig,
       AccountControl.Factory accountControlFactory,
-      Provider<CurrentUser> self) {
+      Provider<CurrentUser> self,
+      ServiceUserClassifier serviceUserClassifier) {
     this.accountLoaderFactory = accountLoaderFactory;
     this.accountQueryBuilder = accountQueryBuilder;
     this.accountIndexRewriter = accountIndexRewriter;
@@ -155,6 +158,7 @@
     this.indexConfig = indexConfig;
     this.accountControlFactory = accountControlFactory;
     this.self = self;
+    this.serviceUserClassifier = serviceUserClassifier;
   }
 
   public interface VisibilityControl {
@@ -200,13 +204,17 @@
             reviewerState, changeNotes, suggestReviewers, projectState, candidateList);
     logger.atFine().log("Sorted recommendations: %s", sortedRecommendations);
 
-    // Filter accounts by visibility and enforce limit
+    // Filter accounts by visibility, skip service users and enforce limit
     List<Account.Id> filteredRecommendations = new ArrayList<>();
     try (Timer0.Context ctx = metrics.filterVisibility.start()) {
       for (Account.Id reviewer : sortedRecommendations) {
         if (filteredRecommendations.size() >= limit) {
           break;
         }
+        if (suggestReviewers.isSkipServiceUsers()
+            && serviceUserClassifier.isServiceUser(reviewer)) {
+          continue;
+        }
         // Check if change is visible to reviewer and if the current user can see reviewer
         if (visibilityControl.isVisibleTo(reviewer)
             && accountControlFactory.get().canSee(reviewer)) {
diff --git a/java/com/google/gerrit/server/restapi/change/SuggestReviewers.java b/java/com/google/gerrit/server/restapi/change/SuggestReviewers.java
index e071c89..71ff493 100644
--- a/java/com/google/gerrit/server/restapi/change/SuggestReviewers.java
+++ b/java/com/google/gerrit/server/restapi/change/SuggestReviewers.java
@@ -31,6 +31,8 @@
 
   private static final int DEFAULT_MAX_SUGGESTED = 10;
 
+  private static final boolean DEFAULT_SKIP_SERVICE_USERS = true;
+
   protected final ReviewersUtil reviewersUtil;
 
   private final boolean suggestAccounts;
@@ -39,6 +41,7 @@
   protected int limit;
   protected String query;
   protected final int maxSuggestedReviewers;
+  protected boolean skipServiceUsers;
 
   @Option(
       name = "--limit",
@@ -78,6 +81,10 @@
     return maxAllowedWithoutConfirmation;
   }
 
+  public boolean isSkipServiceUsers() {
+    return skipServiceUsers;
+  }
+
   @Inject
   public SuggestReviewers(
       AccountVisibility av, @GerritServerConfig Config cfg, ReviewersUtil reviewersUtil) {
@@ -100,6 +107,9 @@
             ReviewerAdder.DEFAULT_MAX_REVIEWERS_WITHOUT_CHECK);
 
     logger.atFine().log("AccountVisibility: %s", av.name());
+
+    this.skipServiceUsers =
+        cfg.getBoolean("suggest", "skipServiceUsers", DEFAULT_SKIP_SERVICE_USERS);
   }
 
   public static GerritConfigListener configListener() {
diff --git a/java/com/google/gerrit/server/restapi/config/GetServerInfo.java b/java/com/google/gerrit/server/restapi/config/GetServerInfo.java
index 5459ede..0a5692e 100644
--- a/java/com/google/gerrit/server/restapi/config/GetServerInfo.java
+++ b/java/com/google/gerrit/server/restapi/config/GetServerInfo.java
@@ -304,6 +304,7 @@
     info.editGpgKeys =
         toBoolean(enableSignedPush && config.getBoolean("gerrit", null, "editGpgKeys", true));
     info.primaryWeblinkName = config.getString("gerrit", null, "primaryWeblinkName");
+    info.instanceId = config.getString("gerrit", null, "instanceId");
     return info;
   }
 
diff --git a/java/com/google/gerrit/server/submit/MergeOp.java b/java/com/google/gerrit/server/submit/MergeOp.java
index 871d8d2..f486650 100644
--- a/java/com/google/gerrit/server/submit/MergeOp.java
+++ b/java/com/google/gerrit/server/submit/MergeOp.java
@@ -189,7 +189,7 @@
       // date by this point.
       ChangeData cd = requireNonNull(changes.get(id), () -> String.format("ChangeData for %s", id));
       return requireNonNull(
-          cd.getSubmitRecords(submitRuleOptions(allowClosed)),
+          cd.submitRecords(submitRuleOptions(allowClosed)),
           "getSubmitRecord only valid after submit rules are evalutated");
     }
 
@@ -549,8 +549,8 @@
             .listener(retryTracker)
             // Up to the entire submit operation is retried, including possibly many projects.
             // Multiply the timeout by the number of projects we're actually attempting to
-            // submit.
-            .defaultTimeoutMultiplier(filteredNoteDbChangeSet.projects().size())
+            // submit. Times 2 to retry more persistently, to increase success rate.
+            .defaultTimeoutMultiplier(filteredNoteDbChangeSet.projects().size() * 2)
             // By default, we only retry lock failures. Here it's better to also retry unexpected
             // runtime exceptions.
             .retryOn(t -> t instanceof RuntimeException)
diff --git a/javatests/com/google/gerrit/acceptance/api/change/SubmitWithStickyApprovalDiffIT.java b/javatests/com/google/gerrit/acceptance/api/change/SubmitWithStickyApprovalDiffIT.java
index eba2634..5ca7310 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/SubmitWithStickyApprovalDiffIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/SubmitWithStickyApprovalDiffIT.java
@@ -21,8 +21,10 @@
 import static com.google.gerrit.server.project.testing.TestLabels.value;
 
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.acceptance.config.GerritConfig;
 import com.google.gerrit.acceptance.testsuite.change.ChangeOperations;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.entities.Change;
@@ -30,6 +32,7 @@
 import com.google.gerrit.entities.LabelType;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
+import com.google.gerrit.extensions.api.changes.ReviewInput.CommentInput;
 import com.google.gerrit.server.patch.filediff.Edit;
 import com.google.gerrit.server.project.testing.TestLabels;
 import com.google.inject.Inject;
@@ -144,6 +147,56 @@
   }
 
   @Test
+  @GerritConfig(name = "change.cumulativeCommentSizeLimit", value = "1k")
+  public void autoGeneratedPostSubmitDiffIsNotPartOfTheCommentSizeLimit() throws Exception {
+    Change.Id changeId =
+        changeOperations.newChange().project(project).file("file").content("content").create();
+    gApi.changes().id(changeId.get()).current().review(ReviewInput.approve());
+    String content = new String(new char[800]).replace("\0", "a");
+    changeOperations.change(changeId).newPatchset().file("file").content(content).create();
+
+    // Post a submit diff that is almost the cumulativeCommentSizeLimit
+    gApi.changes().id(changeId.get()).current().submit();
+    assertThat(Iterables.getLast(gApi.changes().id(changeId.get()).messages()).message)
+        .doesNotContain("many unreviewed changes");
+
+    // unrelated comment and change message posting works fine, since the post submit diff is not
+    // counted towards the cumulativeCommentSizeLimit for unrelated follow-up comments.
+    // 800 + 400 + 400 > 1k, but 400 + 400 < 1k, hence these comments are accepted (the original
+    // 800 is not counted).
+    String message = new String(new char[400]).replace("\0", "a");
+    ReviewInput reviewInput = new ReviewInput().message(message);
+    CommentInput commentInput = new CommentInput();
+    commentInput.line = 1;
+    commentInput.message = message;
+    commentInput.path = "file";
+    reviewInput.comments = ImmutableMap.of("file", ImmutableList.of(commentInput));
+
+    gApi.changes().id(changeId.get()).current().review(reviewInput);
+  }
+
+  @Test
+  @GerritConfig(name = "change.cumulativeCommentSizeLimit", value = "1k")
+  public void postSubmitDiffCannotBeTooBig() throws Exception {
+    Change.Id changeId =
+        changeOperations.newChange().project(project).file("file").content("content").create();
+    gApi.changes().id(changeId.get()).current().review(ReviewInput.approve());
+
+    String content = new String(new char[1100]).replace("\0", "a");
+
+    changeOperations.change(changeId).newPatchset().file("file").content(content).create();
+
+    // Post submit diff is over the cumulativeCommentSizeLimit, so we shorten the message.
+    gApi.changes().id(changeId.get()).current().submit();
+    assertThat(Iterables.getLast(gApi.changes().id(changeId.get()).messages()).message)
+        .isEqualTo(
+            "Change has been successfully merged\n\n1 is the latest approved patch-set.\nThe "
+                + "change was submitted "
+                + "with many unreviewed changes (the diff is too large to show). Please review the "
+                + "diff.");
+  }
+
+  @Test
   public void diffChangeMessageOnSubmitWithStickyVote_addedFile() throws Exception {
     Change.Id changeId = changeOperations.newChange().project(project).create();
     gApi.changes().id(changeId.get()).current().review(ReviewInput.approve());
diff --git a/javatests/com/google/gerrit/acceptance/pgm/BUILD b/javatests/com/google/gerrit/acceptance/pgm/BUILD
index 64bd25c..5b18d02 100644
--- a/javatests/com/google/gerrit/acceptance/pgm/BUILD
+++ b/javatests/com/google/gerrit/acceptance/pgm/BUILD
@@ -27,7 +27,6 @@
     labels = [
         "docker",
         "elastic",
-        "exclusive",
         "pgm",
         "no_windows",
     ],
diff --git a/javatests/com/google/gerrit/acceptance/rest/change/SuggestReviewersIT.java b/javatests/com/google/gerrit/acceptance/rest/change/SuggestReviewersIT.java
index 888878f..ffde622 100644
--- a/javatests/com/google/gerrit/acceptance/rest/change/SuggestReviewersIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/change/SuggestReviewersIT.java
@@ -450,6 +450,23 @@
   }
 
   @Test
+  public void suggestNoServiceAccounts() throws Exception {
+    requestScopeOperations.setApiUser(user.id());
+    String changeIdReviewed = createChangeFromApi();
+    String changeId = createChangeFromApi();
+
+    String name = name("foo");
+    TestAccount foo = accountCreator.create(name);
+    reviewChange(changeIdReviewed, foo);
+
+    assertReviewers(suggestReviewers(changeId, name), ImmutableList.of(foo), ImmutableList.of());
+
+    groupOperations.group(serviceUsersUUID()).forUpdate().addMember(foo.id()).update();
+
+    assertReviewers(suggestReviewers(changeId, name), ImmutableList.of(), ImmutableList.of());
+  }
+
+  @Test
   public void suggestNoExistingReviewers() throws Exception {
     requestScopeOperations.setApiUser(user.id());
     String changeId = createChangeFromApi();
@@ -608,6 +625,13 @@
     return user(name, fullName, name);
   }
 
+  private AccountGroup.UUID serviceUsersUUID() {
+    return groupCache
+        .get(AccountGroup.nameKey("Service Users"))
+        .orElseThrow(() -> new IllegalStateException("unable to find 'Service Users'"))
+        .getGroupUUID();
+  }
+
   private void reviewChange(String changeId, TestAccount reviewer) throws RestApiException {
     gApi.changes().id(changeId).addReviewer(reviewer.id().toString());
   }
diff --git a/javatests/com/google/gerrit/acceptance/rest/config/ServerInfoIT.java b/javatests/com/google/gerrit/acceptance/rest/config/ServerInfoIT.java
index 0a84db4..4738f64 100644
--- a/javatests/com/google/gerrit/acceptance/rest/config/ServerInfoIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/config/ServerInfoIT.java
@@ -74,6 +74,7 @@
   @GerritConfig(name = "gerrit.allProjects", value = "Root")
   @GerritConfig(name = "gerrit.allUsers", value = "Users")
   @GerritConfig(name = "gerrit.reportBugUrl", value = "https://example.com/report")
+  @GerritConfig(name = "gerrit.instanceId", value = "devops-instance")
 
   // suggest
   @GerritConfig(name = "suggest.from", value = "3")
@@ -116,6 +117,7 @@
     assertThat(i.gerrit.allProjects).isEqualTo("Root");
     assertThat(i.gerrit.allUsers).isEqualTo("Users");
     assertThat(i.gerrit.reportBugUrl).isEqualTo("https://example.com/report");
+    assertThat(i.gerrit.instanceId).isEqualTo("devops-instance");
 
     // plugin
     assertThat(i.plugin.jsResourcePaths).isEmpty();
@@ -184,6 +186,7 @@
     assertThat(i.gerrit.allProjects).isEqualTo(AllProjectsNameProvider.DEFAULT);
     assertThat(i.gerrit.allUsers).isEqualTo(AllUsersNameProvider.DEFAULT);
     assertThat(i.gerrit.reportBugUrl).isNull();
+    assertThat(i.gerrit.instanceId).isNull();
 
     // plugin
     assertThat(i.plugin.jsResourcePaths).isEmpty();
diff --git a/javatests/com/google/gerrit/acceptance/rest/project/ProjectLevelConfigIT.java b/javatests/com/google/gerrit/acceptance/rest/project/ProjectLevelConfigIT.java
index 5fd55ec..ffdbd8e 100644
--- a/javatests/com/google/gerrit/acceptance/rest/project/ProjectLevelConfigIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/project/ProjectLevelConfigIT.java
@@ -22,16 +22,23 @@
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
+import com.google.gerrit.server.config.PluginConfigFactory;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.inject.Inject;
 import java.util.Arrays;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.Before;
 import org.junit.Test;
 
 public class ProjectLevelConfigIT extends AbstractDaemonTest {
+  private static final String PLUGIN_NAME = "test-plugin";
+
   @Inject private ProjectOperations projectOperations;
+  @Inject private PluginConfigFactory pluginConfigFactory;
 
   @Before
   public void setUp() throws Exception {
@@ -185,4 +192,27 @@
     ProjectState state = projectCache.get(project).get();
     assertThat(state.getConfig(configName).get().toText()).isEmpty();
   }
+
+  @Test
+  public void emptySubSectionsCanBeRead() throws Exception {
+    updatePluginConfig(project, "[section \"subsection\"]");
+    Config cfg = pluginConfigFactory.getProjectPluginConfigWithInheritance(project, PLUGIN_NAME);
+    assertThat(cfg.getSubsections("section")).containsExactly("subsection");
+  }
+
+  private void updatePluginConfig(Project.NameKey project, String pluginConfig) throws Exception {
+    try (TestRepository<Repository> testRepo =
+        new TestRepository<>(repoManager.openRepository(project))) {
+      Ref ref = testRepo.getRepository().exactRef(RefNames.REFS_CONFIG);
+      RevCommit head = testRepo.getRevWalk().parseCommit(ref.getObjectId());
+      testRepo.update(
+          RefNames.REFS_CONFIG,
+          testRepo
+              .commit()
+              .parent(head)
+              .message("Configure plugin")
+              .add(PLUGIN_NAME + ".config", pluginConfig));
+    }
+    projectCache.evict(project);
+  }
 }
diff --git a/javatests/com/google/gerrit/acceptance/server/change/CommentContextIT.java b/javatests/com/google/gerrit/acceptance/server/change/CommentContextIT.java
index 548e3fe..20b9882 100644
--- a/javatests/com/google/gerrit/acceptance/server/change/CommentContextIT.java
+++ b/javatests/com/google/gerrit/acceptance/server/change/CommentContextIT.java
@@ -31,6 +31,7 @@
 import com.google.gerrit.extensions.client.Side;
 import com.google.gerrit.extensions.common.CommentInfo;
 import com.google.gerrit.extensions.common.ContextLineInfo;
+import com.google.gerrit.server.change.FileContentUtil;
 import com.google.inject.Inject;
 import java.util.ArrayList;
 import java.util.List;
@@ -319,6 +320,82 @@
         IntStream.range(200, 301).boxed().collect(ImmutableList.toImmutableList()));
   }
 
+  @Test
+  public void commentContextReturnsCorrectContentTypeForCommitMessage() throws Exception {
+    PushOneCommit.Result result =
+        createChange(testRepo, "master", SUBJECT, FILE_NAME, FILE_CONTENT, "topic");
+    String changeId = result.getChangeId();
+    String ps1 = result.getCommit().name();
+
+    CommentInput comment = CommentsUtil.newComment(COMMIT_MSG, Side.REVISION, 7, "comment", false);
+    CommentsUtil.addComments(gApi, changeId, ps1, comment);
+
+    List<CommentInfo> comments =
+        gApi.changes().id(changeId).commentsRequest().withContext(true).getAsList();
+
+    assertThat(comments).hasSize(1);
+    assertThat(comments.get(0).path).isEqualTo(COMMIT_MSG);
+    assertThat(comments.get(0).sourceContentType)
+        .isEqualTo(FileContentUtil.TEXT_X_GERRIT_COMMIT_MESSAGE);
+  }
+
+  @Test
+  public void commentContextReturnsCorrectContentType_Java() throws Exception {
+    String javaContent =
+        "public class Main {\n"
+            + " public static void main(String[]args){\n"
+            + " if(args==null){\n"
+            + " System.err.println(\"Something\");\n"
+            + " }\n"
+            + " }\n"
+            + " }";
+    String fileName = "src.java";
+    String changeId = createChangeWithContent(fileName, javaContent, /* line= */ 4);
+
+    List<CommentInfo> comments =
+        gApi.changes().id(changeId).commentsRequest().withContext(true).getAsList();
+
+    assertThat(comments).hasSize(1);
+    assertThat(comments.get(0).path).isEqualTo(fileName);
+    assertThat(comments.get(0).contextLines)
+        .isEqualTo(createContextLines("4", " System.err.println(\"Something\");"));
+    assertThat(comments.get(0).sourceContentType).isEqualTo("text/x-java");
+  }
+
+  @Test
+  public void commentContextReturnsCorrectContentType_Cpp() throws Exception {
+    String cppContent =
+        "#include <iostream>\n"
+            + "\n"
+            + "int main() {\n"
+            + "    std::cout << \"Hello World!\";\n"
+            + "    return 0;\n"
+            + "}";
+    String fileName = "src.cpp";
+    String changeId = createChangeWithContent(fileName, cppContent, /* line= */ 4);
+
+    List<CommentInfo> comments =
+        gApi.changes().id(changeId).commentsRequest().withContext(true).getAsList();
+
+    assertThat(comments).hasSize(1);
+    assertThat(comments.get(0).path).isEqualTo(fileName);
+    assertThat(comments.get(0).contextLines)
+        .isEqualTo(createContextLines("4", "    std::cout << \"Hello World!\";"));
+    assertThat(comments.get(0).sourceContentType).isEqualTo("text/x-c++src");
+  }
+
+  private String createChangeWithContent(String fileName, String fileContent, int line)
+      throws Exception {
+    PushOneCommit.Result result =
+        createChange(testRepo, "master", SUBJECT, fileName, fileContent, "topic");
+    String changeId = result.getChangeId();
+    String ps1 = result.getCommit().name();
+
+    CommentInput comment = CommentsUtil.newComment(fileName, Side.REVISION, line, "comment", false);
+    CommentsUtil.addComments(gApi, changeId, ps1, comment);
+    return changeId;
+  }
+
   private String createChangeWithComment(int startLine, int endLine) throws Exception {
     PushOneCommit.Result result =
         createChange(testRepo, "master", SUBJECT, FILE_NAME, FILE_CONTENT, "topic");
diff --git a/javatests/com/google/gerrit/elasticsearch/BUILD b/javatests/com/google/gerrit/elasticsearch/BUILD
index be35d5a..3036811 100644
--- a/javatests/com/google/gerrit/elasticsearch/BUILD
+++ b/javatests/com/google/gerrit/elasticsearch/BUILD
@@ -55,7 +55,6 @@
 ELASTICSEARCH_TAGS = [
     "docker",
     "elastic",
-    "exclusive",
 ]
 
 [junit_tests(
diff --git a/javatests/com/google/gerrit/server/cache/serialize/CommentContextSerializerTest.java b/javatests/com/google/gerrit/server/cache/serialize/CommentContextSerializerTest.java
index 643c7b7..8fe7662 100644
--- a/javatests/com/google/gerrit/server/cache/serialize/CommentContextSerializerTest.java
+++ b/javatests/com/google/gerrit/server/cache/serialize/CommentContextSerializerTest.java
@@ -14,7 +14,7 @@
   @Test
   public void roundTripValue() {
     CommentContext commentContext =
-        CommentContext.create(ImmutableMap.of(1, "line_1", 2, "line_2"));
+        CommentContext.create(ImmutableMap.of(1, "line_1", 2, "line_2"), "text/x-java");
 
     byte[] serialized = INSTANCE.serialize(commentContext);
     CommentContext deserialized = INSTANCE.deserialize(serialized);
diff --git a/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java
index 44ea55a..17fd959 100644
--- a/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java
+++ b/javatests/com/google/gerrit/server/cache/serialize/entities/FileDiffOutputSerializerTest.java
@@ -19,10 +19,12 @@
 import com.google.common.collect.ImmutableList;
 import com.google.gerrit.entities.Patch.ChangeType;
 import com.google.gerrit.entities.Patch.PatchType;
+import com.google.gerrit.server.patch.ComparisonType;
 import com.google.gerrit.server.patch.filediff.Edit;
 import com.google.gerrit.server.patch.filediff.FileDiffOutput;
 import com.google.gerrit.server.patch.filediff.TaggedEdit;
 import java.util.Optional;
+import org.eclipse.jgit.lib.ObjectId;
 import org.junit.Test;
 
 public class FileDiffOutputSerializerTest {
@@ -35,6 +37,9 @@
 
     FileDiffOutput fileDiff =
         FileDiffOutput.builder()
+            .oldCommitId(ObjectId.fromString("dd4d2a1498870ca5fe415b33f65d052d69d9eaf5"))
+            .newCommitId(ObjectId.fromString("0cfaab3f2ba76f71798da0a2651f41be8d45f842"))
+            .comparisonType(ComparisonType.againstOtherPatchSet())
             .oldPath(Optional.of("old_file_path.txt"))
             .newPath(Optional.empty())
             .changeType(ChangeType.DELETED)
diff --git a/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java b/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
index 7efcb4b..48bd321 100644
--- a/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
+++ b/javatests/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
@@ -705,6 +705,24 @@
   }
 
   @Test
+  public void byParentOf() throws Exception {
+    TestRepository<Repo> repo1 = createProject("repo1");
+    RevCommit commit1 = repo1.parseBody(repo1.commit().message("message").create());
+    Change change1 = insert(repo1, newChangeForCommit(repo1, commit1));
+    RevCommit commit2 = repo1.parseBody(repo1.commit(commit1));
+    Change change2 = insert(repo1, newChangeForCommit(repo1, commit2));
+    RevCommit commit3 = repo1.parseBody(repo1.commit(commit1, commit2));
+    Change change3 = insert(repo1, newChangeForCommit(repo1, commit3));
+
+    assertQuery("parentof:" + change1.getId().get());
+    assertQuery("parentof:" + change1.getKey().get());
+    assertQuery("parentof:" + change2.getId().get(), change1);
+    assertQuery("parentof:" + change2.getKey().get(), change1);
+    assertQuery("parentof:" + change3.getId().get(), change2, change1);
+    assertQuery("parentof:" + change3.getKey().get(), change2, change1);
+  }
+
+  @Test
   public void byParentProject() throws Exception {
     TestRepository<Repo> repo1 = createProject("repo1");
     TestRepository<Repo> repo2 = createProject("repo2", "repo1");
diff --git a/modules/jgit b/modules/jgit
index 4560bdf..9bfb0f3 160000
--- a/modules/jgit
+++ b/modules/jgit
@@ -1 +1 @@
-Subproject commit 4560bdf7e2e3c16a7c7bb3f2fcf067bb1eee26fb
+Subproject commit 9bfb0f3a4ec856dcbebb477a1ee8803a3c47c194
diff --git a/plugins/replication b/plugins/replication
index ab80790..14766e7 160000
--- a/plugins/replication
+++ b/plugins/replication
@@ -1 +1 @@
-Subproject commit ab8079055a92fa4068a2982306c11425f347e12f
+Subproject commit 14766e75f91886ab48951035d59a78c8c3f07471
diff --git a/polygerrit-ui/app/api/checks.ts b/polygerrit-ui/app/api/checks.ts
index 799d1f7..4a5ef7e 100644
--- a/polygerrit-ui/app/api/checks.ts
+++ b/polygerrit-ui/app/api/checks.ts
@@ -247,7 +247,7 @@
   checkName: string | undefined,
   /** Identical to 'name' property of Action entity. */
   actionName: string
-) => Promise<ActionResult>;
+) => Promise<ActionResult> | undefined;
 
 export interface ActionResult {
   /** An empty errorMessage means success. */
diff --git a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
index 5305cea..f2b4c89 100644
--- a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
+++ b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
@@ -400,7 +400,7 @@
       }
       return '';
     }
-    // TODO(TS): The following condtion seems always false, because params
+    // TODO(TS): The following condition seems always false, because params
     // never has detailType property. Remove it.
     if (
       ((params as unknown) as AdminSubsectionLink).detailType &&
diff --git a/polygerrit-ui/app/elements/admin/gr-rule-editor/gr-rule-editor_test.js b/polygerrit-ui/app/elements/admin/gr-rule-editor/gr-rule-editor_test.js
index b0065d9..9cc6357 100644
--- a/polygerrit-ui/app/elements/admin/gr-rule-editor/gr-rule-editor_test.js
+++ b/polygerrit-ui/app/elements/admin/gr-rule-editor/gr-rule-editor_test.js
@@ -192,7 +192,7 @@
       };
       element.section = 'refs/*';
 
-      // Typically called on ready since elements will have properies defined
+      // Typically called on ready since elements will have properties defined
       // by the parent element.
       element._setupValues(element.rule);
       flush();
diff --git a/polygerrit-ui/app/elements/change-list/gr-create-change-help/gr-create-change-help_html.ts b/polygerrit-ui/app/elements/change-list/gr-create-change-help/gr-create-change-help_html.ts
index 9812933..add7ca5 100644
--- a/polygerrit-ui/app/elements/change-list/gr-create-change-help/gr-create-change-help_html.ts
+++ b/polygerrit-ui/app/elements/change-list/gr-create-change-help/gr-create-change-help_html.ts
@@ -36,7 +36,7 @@
       width: 10em;
     }
     #graphic iron-icon {
-      color: #9e9e9e;
+      color: var(--gray-foreground);
       height: 5em;
       width: 5em;
     }
diff --git a/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view.ts b/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view.ts
index 9240905..a34bd63 100644
--- a/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view.ts
+++ b/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view.ts
@@ -58,7 +58,7 @@
 import {firePageError, fireTitleChange} from '../../../utils/event-util';
 import {GerritView} from '../../../services/router/router-model';
 
-const PROJECT_PLACEHOLDER_PATTERN = /\$\{project\}/g;
+const PROJECT_PLACEHOLDER_PATTERN = /\${project}/g;
 const RELOAD_DASHBOARD_INTERVAL_MS = 10 * 1000;
 
 export interface GrDashboardView {
@@ -380,6 +380,19 @@
       e.detail.change._number,
       e.detail.starred
     );
+    // When a change is updated the same change may appear elsewhere in the
+    // dashboard (but is not the same object), so we must update other
+    // occurrences of the same change.
+    this._results?.forEach((dashboardChange, dashboardIndex) =>
+      dashboardChange.results.forEach((change, changeIndex) => {
+        if (change.id === e.detail.change.id) {
+          this.set(
+            `_results.${dashboardIndex}.results.${changeIndex}.starred`,
+            e.detail.starred
+          );
+        }
+      })
+    );
   }
 
   _handleToggleReviewed(e: CustomEvent<ChangeListToggleReviewedDetail>) {
@@ -387,6 +400,19 @@
       e.detail.change._number,
       e.detail.reviewed
     );
+    // When a change is updated the same change may appear elsewhere in the
+    // dashboard (but is not the same object), so we must update other
+    // occurrences of the same change.
+    this._results?.forEach((dashboardChange, dashboardIndex) =>
+      dashboardChange.results.forEach((change, changeIndex) => {
+        if (change.id === e.detail.change.id) {
+          this.set(
+            `_results.${dashboardIndex}.results.${changeIndex}.reviewed`,
+            e.detail.reviewed
+          );
+        }
+      })
+    );
   }
 
   /**
diff --git a/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view_test.js b/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view_test.js
index 47f885b..a5de72b 100644
--- a/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view_test.js
+++ b/polygerrit-ui/app/elements/change-list/gr-dashboard-view/gr-dashboard-view_test.js
@@ -332,6 +332,56 @@
     });
   });
 
+  test('toggling star will update change everywhere', () => {
+    // It is important that the same change is represented by multiple objects
+    // and all are updated.
+    const change = {id: '5', starred: false};
+    const sameChange = {id: '5', starred: false};
+    const differentChange = {id: '4', starred: false};
+    element._results = [
+      {query: 'has:draft', results: [change]},
+      {query: 'is:open', results: [sameChange, differentChange]},
+    ];
+
+    element._handleToggleStar(
+        new CustomEvent('toggle-star', {
+          detail: {
+            change,
+            starred: true,
+          },
+        })
+    );
+
+    assert.isTrue(change.starred);
+    assert.isTrue(sameChange.starred);
+    assert.isFalse(differentChange.starred);
+  });
+
+  test('toggling reviewed will update change everywhere', () => {
+    // It is important that the same change is represented by multiple objects
+    // and all are updated.
+    const change = {id: '5', reviewed: false};
+    const sameChange = {id: '5', reviewed: false};
+    const differentChange = {id: '4', reviewed: false};
+    element._results = [
+      {query: 'has:draft', results: [change]},
+      {query: 'is:open', results: [sameChange, differentChange]},
+    ];
+
+    element._handleToggleReviewed(
+        new CustomEvent('toggle-reviewed', {
+          detail: {
+            change,
+            reviewed: true,
+          },
+        })
+    );
+
+    assert.isTrue(change.reviewed);
+    assert.isTrue(sameChange.reviewed);
+    assert.isFalse(differentChange.reviewed);
+  });
+
   test('_showNewUserHelp', () => {
     element._loading = false;
     element._showNewUserHelp = false;
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
index c3858d8..87b09c7 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
@@ -2068,10 +2068,10 @@
    *
    */
   _waitForChangeReachable(changeNum: NumericChangeId) {
-    let attempsRemaining = AWAIT_CHANGE_ATTEMPTS;
+    let attemptsRemaining = AWAIT_CHANGE_ATTEMPTS;
     return new Promise(resolve => {
       const check = () => {
-        attempsRemaining--;
+        attemptsRemaining--;
         // Pass a no-op error handler to avoid the "not found" error toast.
         this.restApiService
           .getChange(changeNum, () => {})
@@ -2082,7 +2082,7 @@
               return;
             }
 
-            if (attempsRemaining) {
+            if (attemptsRemaining) {
               this.async(check, AWAIT_CHANGE_TIMEOUT_MS);
             } else {
               resolve(false);
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.js b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.js
index 6c9a27d..fbb70b7 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.js
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.js
@@ -2110,7 +2110,7 @@
 
       element = basicFixture.instantiate();
       // getChangeRevisionActions is not called without
-      // set the following properies
+      // set the following properties
       element.change = {};
       element.changeNum = '42';
       element.latestPatchNum = '2';
diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata.ts b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata.ts
index ef4d323..68e2368 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata.ts
@@ -210,6 +210,8 @@
 
   restApiService = appContext.restApiService;
 
+  private readonly reporting = appContext.reportingService;
+
   /** @override */
   ready() {
     super.ready();
@@ -567,6 +569,10 @@
 
   _onShowAllClick() {
     this._showAllSections = !this._showAllSections;
+    this.reporting.reportInteraction('toggle show all button', {
+      sectionName: 'metadata',
+      toState: this._showAllSections ? 'Show all' : 'Show less',
+    });
   }
 
   /**
diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
index c5c73c5..59bf8ad 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
@@ -78,7 +78,7 @@
     }
     .icon.help,
     .icon.notTrusted {
-      color: #ffa62f;
+      color: var(--warning-foreground);
     }
     .icon.invalid {
       color: var(--negative-red-text-color);
@@ -87,7 +87,7 @@
       color: var(--positive-green-text-color);
     }
     .parentList.notCurrent.nonMerge #parentNotCurrentMessage {
-      --arrow-color: #ffa62f;
+      --arrow-color: var(--warning-foreground);
       display: inline-block;
     }
     .separatedSection {
diff --git a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements.ts b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements.ts
index c0e87f3..e3fdf7a 100644
--- a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements.ts
@@ -37,6 +37,7 @@
 import {PolymerDeepPropertyChange} from '@polymer/polymer/interfaces';
 import {appContext} from '../../../services/app-context';
 import {KnownExperimentId} from '../../../services/flags/flags';
+import {labelCompare} from '../../../utils/label-util';
 
 interface ChangeRequirement extends Requirement {
   satisfied: boolean;
@@ -93,6 +94,8 @@
     KnownExperimentId.NEW_CHANGE_SUMMARY_UI
   );
 
+  private readonly reporting = appContext.reportingService;
+
   _computeShowWip(change: ChangeInfo) {
     return change.work_in_progress;
   }
@@ -136,7 +139,7 @@
     const labels = labelsRecord.base || {};
     const allLabels: Label[] = [];
 
-    for (const label of Object.keys(labels).sort()) {
+    for (const label of Object.keys(labels).sort(labelCompare)) {
       allLabels.push({
         labelName: label,
         icon: this._computeLabelIcon(labels[label]),
@@ -192,6 +195,10 @@
 
   _handleShowHide() {
     this._showOptionalLabels = !this._showOptionalLabels;
+    this.reporting.reportInteraction('toggle show all button', {
+      sectionName: 'optional labels',
+      toState: this._showOptionalLabels ? 'Show all' : 'Show less',
+    });
   }
 
   _computeSubmitRequirementEndpoint(item: ChangeRequirement | ChangeWIP) {
diff --git a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.ts b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.ts
index e02b337..a502949 100644
--- a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.ts
@@ -23,7 +23,7 @@
       width: 100%;
     }
     .status {
-      color: #ffa62f;
+      color: var(--warning-foreground);
       display: inline-block;
       text-align: center;
       vertical-align: top;
diff --git a/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts b/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
index 4af51a9..427924e 100644
--- a/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-summary/gr-change-summary.ts
@@ -22,7 +22,8 @@
 import {KnownExperimentId} from '../../../services/flags/flags';
 import {
   allRuns$,
-  aPluginHasRegistered,
+  aPluginHasRegistered$,
+  someProvidersAreLoading$,
 } from '../../../services/checks/checks-model';
 import {
   Category,
@@ -56,7 +57,7 @@
 import {notUndefined} from '../../../types/types';
 import {uniqueDefinedAvatar} from '../../../utils/account-util';
 import {PrimaryTab} from '../../../constants/constants';
-import {CommentTabState} from '../../../types/events';
+import {ChecksTabState, CommentTabState} from '../../../types/events';
 
 export enum SummaryChipStyles {
   INFO = 'info',
@@ -76,6 +77,8 @@
   @property()
   category?: CommentTabState;
 
+  private readonly reporting = appContext.reportingService;
+
   static get styles() {
     return [
       sharedStyles,
@@ -110,13 +113,6 @@
         .summaryChip.check iron-icon {
           color: var(--gray-foreground);
         }
-        .summaryChip.info {
-          border-color: var(--info-deemphasized-foreground;
-          background-color: var(--info-deemphasized-background);
-        }
-        .summaryChip.info iron-icon {
-          color: var(--info-deemphasized-foreground);
-        }
       `,
     ];
   }
@@ -137,6 +133,9 @@
   private handleClick(e: MouseEvent) {
     e.stopPropagation();
     e.preventDefault();
+    this.reporting.reportInteraction('comment chip click', {
+      category: this.category,
+    });
     fireShowPrimaryTab(this, PrimaryTab.COMMENT_THREADS, true, {
       commentTab: this.category,
     });
@@ -229,19 +228,13 @@
     const chipClass = `checksChip font-small ${this.icon}`;
     const grIcon = `gr-icons:${this.icon}`;
     return html`
-      <div class="${chipClass}" role="button" @click="${this.handleClick}">
+      <div class="${chipClass}" role="button">
         <iron-icon icon="${grIcon}"></iron-icon>
         <div class="text">${this.text}</div>
         <slot></slot>
       </div>
     `;
   }
-
-  private handleClick(e: MouseEvent) {
-    e.stopPropagation();
-    e.preventDefault();
-    fireShowPrimaryTab(this, PrimaryTab.CHECKS);
-  }
 }
 
 /** What is the maximum number of expanded checks chips? */
@@ -268,13 +261,17 @@
   @property()
   showChecksSummary = false;
 
+  @property()
+  someProvidersAreLoading = false;
+
   /** Is reset when rendering beings and decreases while chips are rendered. */
   private detailsQuota = DETAILS_QUOTA;
 
   constructor() {
     super();
     this.subscribe('runs', allRuns$);
-    this.subscribe('showChecksSummary', aPluginHasRegistered);
+    this.subscribe('showChecksSummary', aPluginHasRegistered$);
+    this.subscribe('someProvidersAreLoading', someProvidersAreLoading$);
   }
 
   static get styles() {
@@ -318,14 +315,15 @@
 
   renderChecksZeroState() {
     if (this.runs.some(isRunningOrHasCompleted)) return;
-    return html`<span class="font-small zeroState">No results</span>`;
+    const msg = this.someProvidersAreLoading ? 'Loading...' : 'No results';
+    return html`<span class="font-small zeroState">${msg}</span>`;
   }
 
   renderChecksChipForCategory(category: Category) {
     const icon = iconForCategory(category);
     const runs = this.runs.filter(run => hasResultsOf(run, category));
     const count = (run: CheckRun) => getResultsOf(run, category);
-    return this.renderChecksChip(icon, runs, count);
+    return this.renderChecksChip(icon, runs, category, count);
   }
 
   renderChecksChipForStatus(
@@ -334,12 +332,13 @@
   ) {
     const icon = iconForStatus(status);
     const runs = this.runs.filter(filter);
-    return this.renderChecksChip(icon, runs, () => []);
+    return this.renderChecksChip(icon, runs, status, () => []);
   }
 
   renderChecksChip(
     icon: string,
     runs: CheckRun[],
+    statusOrCategory: RunStatus | Category,
     resultFilter: (run: CheckRun) => CheckResult[]
   ) {
     if (runs.length === 0) {
@@ -359,9 +358,10 @@
           class="${icon}"
           .icon="${icon}"
           .text="${text}"
+          @click="${() => this.onChipClick({checkName: run.checkName})}"
           >${links.map(
             link => html`
-              <a href="${link.url}" target="_blank" @click="${this.onClick}"
+              <a href="${link.url}" target="_blank" @click="${this.onLinkClick}"
                 ><iron-icon class="launch" icon="gr-icons:launch"></iron-icon
               ></a>
             `
@@ -380,11 +380,18 @@
       class="${icon}"
       .icon="${icon}"
       .text="${sum}"
+      @click="${() => this.onChipClick({statusOrCategory})}"
     ></gr-checks-chip>`;
   }
 
-  private onClick(e: MouseEvent) {
-    // Prevents handleClick() from reacting to <a> link clicks.
+  private onChipClick(state: ChecksTabState) {
+    fireShowPrimaryTab(this, PrimaryTab.CHECKS, true, {
+      checksTab: state,
+    });
+  }
+
+  private onLinkClick(e: MouseEvent) {
+    // Prevents onChipClick() from reacting to <a> link clicks.
     e.stopPropagation();
   }
 
@@ -436,7 +443,6 @@
               ><gr-summary-chip
                 styleType=${SummaryChipStyles.WARNING}
                 category=${CommentTabState.UNRESOLVED}
-                icon="message"
                 ?hidden=${!countUnresolvedComments}
               >
                 ${unresolvedAuthors.map(
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
index 3d7646f..ab1c48f 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
@@ -171,7 +171,7 @@
 import {fireTitleChange} from '../../../utils/event-util';
 import {GerritView} from '../../../services/router/router-model';
 import {takeUntil} from 'rxjs/operators';
-import {aPluginHasRegistered} from '../../../services/checks/checks-model';
+import {aPluginHasRegistered$} from '../../../services/checks/checks-model';
 import {Subject} from 'rxjs';
 import {GrRelatedChangesListExperimental} from '../gr-related-changes-list-experimental/gr-related-changes-list-experimental';
 
@@ -274,11 +274,13 @@
    * @event show-auth-required
    */
 
-  reporting = appContext.reportingService;
+  private readonly reporting = appContext.reportingService;
 
-  flagsService = appContext.flagsService;
+  private readonly flagsService = appContext.flagsService;
 
-  readonly jsAPI = appContext.jsApiService;
+  private readonly jsAPI = appContext.jsApiService;
+
+  private readonly changeService = appContext.changeService;
 
   /**
    * URL params passed from the router.
@@ -594,7 +596,7 @@
   /** @override */
   ready() {
     super.ready();
-    aPluginHasRegistered.pipe(takeUntil(this.disconnected$)).subscribe(b => {
+    aPluginHasRegistered$.pipe(takeUntil(this.disconnected$)).subscribe(b => {
       this._showChecksTab = b;
     });
     this._isNewChangeSummaryUiEnabled = this.flagsService.isEnabled(
@@ -823,8 +825,11 @@
       paperTabs.scrollIntoView();
     }
     if (paperTabs.selected !== activeIndex) {
+      // paperTabs.selected is undefined during rendering
+      if (paperTabs.selected !== undefined) {
+        this.reporting.reportInteraction('show-tab', {tabName});
+      }
       paperTabs.selected = activeIndex;
-      this.reporting.reportInteraction('show-tab', {tabName});
     }
     return tabName;
   }
@@ -2022,6 +2027,7 @@
         this._lineHeight = Number(lineHeight.slice(0, lineHeight.length - 2));
 
         this._change = change;
+        this.changeService.updateChange(change);
         if (
           !this._patchRange ||
           !this._patchRange.patchNum ||
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
index f3fb860..08c04e8 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
@@ -690,7 +690,10 @@
         is="dom-if"
         if="[[_isTabActive(_constants.PrimaryTab.CHECKS, _activeTabs)]]"
       >
-        <gr-checks-tab id="checksTab"></gr-checks-tab>
+        <gr-checks-tab
+          id="checksTab"
+          tab-state="[[_tabState.checksTab]]"
+        ></gr-checks-tab>
       </template>
       <template
         is="dom-if"
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
index 99e5356..ae446cd 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.ts
@@ -105,6 +105,7 @@
 import {GerritView} from '../../../services/router/router-model';
 import {ParsedChangeInfo} from '../../../types/types';
 import {GrRelatedChangesList} from '../gr-related-changes-list/gr-related-changes-list';
+import {appContext} from '../../../services/app-context';
 
 const pluginApi = _testOnly_initGerritPluginApi();
 const fixture = fixtureFromElement('gr-change-view');
@@ -2766,7 +2767,7 @@
     element._change = {...change};
     element._patchRange = {patchNum: 4 as PatchSetNum};
     element._mergeable = true;
-    const showStub = sinon.stub(element.jsAPI, 'handleEvent');
+    const showStub = sinon.stub(appContext.jsApiService, 'handleEvent');
     element._sendShowChangeEvent();
     assert.isTrue(showStub.calledOnce);
     assert.equal(showStub.lastCall.args[0], EventType.SHOW_CHANGE);
@@ -2968,11 +2969,11 @@
 
     test("don't report changeDisplayed on reply", done => {
       const changeDisplayStub = sinon.stub(
-        element.reporting,
+        appContext.reportingService,
         'changeDisplayed'
       );
       const changeFullyLoadedStub = sinon.stub(
-        element.reporting,
+        appContext.reportingService,
         'changeFullyLoaded'
       );
       element._handleReplySent();
@@ -2985,11 +2986,11 @@
 
     test('report changeDisplayed on _paramsChanged', done => {
       const changeDisplayStub = sinon.stub(
-        element.reporting,
+        appContext.reportingService,
         'changeDisplayed'
       );
       const changeFullyLoadedStub = sinon.stub(
-        element.reporting,
+        appContext.reportingService,
         'changeFullyLoaded'
       );
       element._paramsChanged({
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog.ts b/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog.ts
index 225e3e9..ebcabbf 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog.ts
@@ -38,6 +38,7 @@
 import {AutocompleteSuggestion} from '../../shared/gr-autocomplete/gr-autocomplete';
 import {HttpMethod, ChangeStatus} from '../../../constants/constants';
 import {dom, EventApi} from '@polymer/polymer/lib/legacy/polymer.dom';
+import {fireEvent} from '../../../utils/event-util';
 
 const SUGGESTIONS_LIMIT = 15;
 const CHANGE_SUBJECT_LIMIT = 50;
@@ -264,10 +265,12 @@
 
   _handlecherryPickSingleChangeClicked() {
     this._cherryPickType = CherryPickType.SINGLE_CHANGE;
+    fireEvent(this, 'iron-resize');
   }
 
   _handlecherryPickTopicClicked() {
     this._cherryPickType = CherryPickType.TOPIC;
+    fireEvent(this, 'iron-resize');
   }
 
   @observe('changeStatus', 'commitNum', 'commitMessage')
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog_html.ts b/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog_html.ts
index 4de395c..6c0099e 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog_html.ts
@@ -46,11 +46,12 @@
     }
     .cherryPickTopicLayout {
       display: flex;
+      align-items: center;
+      margin-bottom: var(--spacing-m);
     }
     .cherryPickSingleChange,
     .cherryPickTopic {
       margin-left: var(--spacing-m);
-      margin-bottom: var(--spacing-m);
     }
     .cherry-pick-topic-message {
       margin-bottom: var(--spacing-m);
diff --git a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_html.ts b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_html.ts
index 99094d2..29b3752 100644
--- a/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-confirm-submit-dialog/gr-confirm-submit-dialog_html.ts
@@ -25,7 +25,7 @@
       margin-bottom: var(--spacing-l);
     }
     .warningBeforeSubmit {
-      color: var(--error-text-color);
+      color: var(--warning-foreground);
       vertical-align: top;
       margin-right: var(--spacing-s);
     }
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
index a5c0624..c2947a6 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.ts
@@ -803,7 +803,7 @@
   }
 
   /**
-   * Handle all events from the file list dom-repeat so event handleers don't
+   * Handle all events from the file list dom-repeat so event handlers don't
    * have to get registered for potentially very long lists.
    */
   _handleFileListClick(e: MouseEvent) {
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.ts b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.ts
index 23718fa..c57a2d5 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.ts
@@ -154,7 +154,7 @@
       padding-left: var(--spacing-s);
     }
     .drafts {
-      color: #c62828;
+      color: var(--error-foreground);
       font-weight: var(--font-weight-bold);
     }
     .show-hide-icon:focus {
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
index 285b73f..80d8729 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.js
@@ -1244,7 +1244,7 @@
       // are no deletions.
       assert.equal(element._computeBarAdditionWidth(file, stats), 30);
 
-      // If there are no insetions, there is no width.
+      // If there are no insertions, there is no width.
       stats.maxInserted = 0;
       assert.equal(element._computeBarAdditionWidth(file, stats), 0);
 
diff --git a/polygerrit-ui/app/elements/change/gr-label-scores/gr-label-scores.ts b/polygerrit-ui/app/elements/change/gr-label-scores/gr-label-scores.ts
index a966186..661cd1a 100644
--- a/polygerrit-ui/app/elements/change/gr-label-scores/gr-label-scores.ts
+++ b/polygerrit-ui/app/elements/change/gr-label-scores/gr-label-scores.ts
@@ -37,6 +37,7 @@
 } from '../gr-label-score-row/gr-label-score-row';
 import {PolymerDeepPropertyChange} from '@polymer/polymer/interfaces';
 import {appContext} from '../../../services/app-context';
+import {labelCompare} from '../../../utils/label-util';
 
 @customElement('gr-label-scores')
 export class GrLabelScores extends GestureEventListeners(
@@ -147,7 +148,7 @@
     if (!labelRecord?.base) return [];
     const labelsObj = labelRecord.base;
     return Object.keys(labelsObj)
-      .sort()
+      .sort(labelCompare)
       .map(key => {
         return {
           name: key,
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
index 2fe409a..f913459 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
@@ -54,7 +54,7 @@
 } from '../../../utils/patch-set-util';
 import {isServiceUser} from '../../../utils/account-util';
 
-const PATCH_SET_PREFIX_PATTERN = /^(?:Uploaded\s*)?(?:P|p)atch (?:S|s)et \d+:\s*(.*)/;
+const PATCH_SET_PREFIX_PATTERN = /^(?:Uploaded\s*)?[Pp]atch [Ss]et \d+:\s*(.*)/;
 const LABEL_TITLE_SCORE_PATTERN = /^(-?)([A-Za-z0-9-]+?)([+-]\d+)?[.]?$/;
 const UPLOADED_NEW_PATCHSET_PATTERN = /Uploaded patch set (\d+)./;
 const MERGED_PATCHSET_PATTERN = /(\d+) is the latest approved patch-set/;
@@ -484,7 +484,7 @@
   _handleAnchorClick(e: Event) {
     e.preventDefault();
     // The element which triggers _handleAnchorClick is rendered only if
-    // message.id defined: the elemenet is wrapped in dom-if if="[[message.id]]"
+    // message.id defined: the element is wrapped in dom-if if="[[message.id]]"
     const detail: MessageAnchorTapDetail = {
       id: this.message!.id,
     };
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
index b93040b..c018443 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
@@ -61,7 +61,7 @@
       font-weight: var(--font-weight-bold);
     }
     .message {
-      --gr-formatted-text-prose-max-width: 80ch;
+      --gr-formatted-text-prose-max-width: 120ch;
     }
     .collapsed .message {
       max-width: none;
@@ -305,7 +305,7 @@
           </gr-button>
         </template>
         <template is="dom-if" if="[[message._revision_number]]">
-          <span class="patchset">[[message._revision_number]]</span>
+          <span class="patchset">[[message._revision_number]] |</span>
         </template>
         <template is="dom-if" if="[[!message.id]]">
           <span class="date">
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
index 9877a95..bc3f167 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
@@ -118,7 +118,7 @@
 
 /**
  * If messages have the same tag, then that influences grouping and whether
- * a message is initally hidden or not, see isImportant(). So we are applying
+ * a message is initially hidden or not, see isImportant(). So we are applying
  * some "magic" rules here in order to hide exactly the right messages.
  *
  * 1. If a message does not have a tag, but is associated with robot comments,
@@ -263,7 +263,7 @@
   _combinedMessages: CombinedMessage[] = [];
 
   @property({type: Object, computed: '_computeLabelExtremes(labels.*)'})
-  _labelExtremes: {[lableName: string]: VotingRangeInfo} = {};
+  _labelExtremes: {[labelName: string]: VotingRangeInfo} = {};
 
   private readonly reporting = appContext.reportingService;
 
@@ -466,7 +466,7 @@
       LabelNameToInfoMap
     >
   ) {
-    const extremes: {[lableName: string]: VotingRangeInfo} = {};
+    const extremes: {[labelName: string]: VotingRangeInfo} = {};
     const labels = labelRecord.base;
     if (!labels) {
       return extremes;
diff --git a/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-change.ts b/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-change.ts
index 3ed545e..7b698f1 100644
--- a/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-change.ts
+++ b/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-change.ts
@@ -77,10 +77,10 @@
           margin-left: var(--spacing-xs);
         }
         .notCurrent {
-          color: #e65100;
+          color: var(--warning-foreground);
         }
         .indirectAncestor {
-          color: #33691e;
+          color: var(--indirect-ancestor-text-color);
         }
         .submittableCheck {
           padding-left: var(--spacing-s);
diff --git a/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-changes-list-experimental.ts b/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-changes-list-experimental.ts
index e921979..214271af 100644
--- a/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-changes-list-experimental.ts
+++ b/polygerrit-ui/app/elements/change/gr-related-changes-list-experimental/gr-related-changes-list-experimental.ts
@@ -429,6 +429,8 @@
   @property()
   length = 0;
 
+  private readonly reporting = appContext.reportingService;
+
   static get styles() {
     return [
       sharedStyles,
@@ -509,6 +511,10 @@
   private toggle(e: MouseEvent) {
     e.stopPropagation();
     this.showAll = !this.showAll;
+    this.reporting.reportInteraction('toggle show all button', {
+      sectionName: this.title,
+      toState: this.showAll ? 'Show all' : 'Show less',
+    });
   }
 }
 
diff --git a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.ts b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.ts
index 9941fa9..2f53319 100644
--- a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.ts
@@ -66,10 +66,10 @@
       margin-left: var(--spacing-xs);
     }
     .notCurrent {
-      color: #e65100;
+      color: var(--warning-foreground);
     }
     .indirectAncestor {
-      color: #33691e;
+      color: var(--indirect-ancestor-text-color);
     }
     .submittableCheck {
       padding-left: var(--spacing-s);
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
index 705a402..a8e89b6 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog.ts
@@ -784,7 +784,7 @@
   }
 
   _handle400Error(r?: Response | null) {
-    if (!r) throw new Error('Reponse is empty.');
+    if (!r) throw new Error('Response is empty.');
     let response: Response = r;
     // A call to _saveReview could fail with a server error if erroneous
     // reviewers were requested. This is signalled with a 400 Bad Request
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
index 6682bfb..0575239 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.js
@@ -1276,7 +1276,7 @@
         'Send and Start review');
   });
 
-  test('_handle400Error reviewrs and CCs', done => {
+  test('_handle400Error reviewers and CCs', done => {
     const error1 = 'error 1';
     const error2 = 'error 2';
     const error3 = 'error 3';
diff --git a/polygerrit-ui/app/elements/checks/gr-checks-results.ts b/polygerrit-ui/app/elements/checks/gr-checks-results.ts
index e448374..ef2430c 100644
--- a/polygerrit-ui/app/elements/checks/gr-checks-results.ts
+++ b/polygerrit-ui/app/elements/checks/gr-checks-results.ts
@@ -24,7 +24,14 @@
   query,
 } from 'lit-element';
 import {GrLitElement} from '../lit/gr-lit-element';
-import {Category, CheckRun, Link, RunStatus, Tag} from '../../api/checks';
+import {
+  Category,
+  CheckRun,
+  Link,
+  LinkIcon,
+  RunStatus,
+  Tag,
+} from '../../api/checks';
 import {sharedStyles} from '../../styles/shared-styles';
 import {RunResult} from '../../services/checks/checks-model';
 import {
@@ -35,6 +42,7 @@
 } from '../../services/checks/checks-util';
 import {assertIsDefined} from '../../utils/common-util';
 import {whenVisible} from '../../utils/dom-util';
+import {durationString} from '../../utils/date-util';
 
 @customElement('gr-result-row')
 class GrResultRow extends GrLitElement {
@@ -295,6 +303,8 @@
   @property()
   runs: CheckRun[] = [];
 
+  private isSectionExpanded = new Map<Category | 'SUCCESS', boolean>();
+
   static get styles() {
     return [
       sharedStyles,
@@ -312,23 +322,36 @@
           margin-top: var(--spacing-l);
           margin-left: var(--spacing-l);
           text-transform: capitalize;
+          cursor: default;
         }
-        .categoryHeader iron-icon {
+        .categoryHeader .expandIcon {
+          width: var(--line-height-h3);
+          height: var(--line-height-h3);
+          margin-right: var(--spacing-s);
+        }
+        .categoryHeader .statusIcon {
           position: relative;
-          top: 1px;
+          top: 2px;
         }
-        .categoryHeader iron-icon.error {
+        .categoryHeader .statusIcon.error {
           color: var(--error-foreground);
         }
-        .categoryHeader iron-icon.warning {
+        .categoryHeader .statusIcon.warning {
           color: var(--warning-foreground);
         }
-        .categoryHeader iron-icon.info {
+        .categoryHeader .statusIcon.info {
           color: var(--info-foreground);
         }
-        .categoryHeader iron-icon.success {
+        .categoryHeader .statusIcon.success {
           color: var(--success-foreground);
         }
+        .collapsed table {
+          display: none;
+        }
+        .collapsed {
+          border-bottom: 1px solid var(--border-color);
+          padding-bottom: var(--spacing-m);
+        }
         .noCompleted {
           margin-top: var(--spacing-l);
         }
@@ -354,7 +377,7 @@
       ${this.renderFilter()} ${this.renderNoCompleted()}
       ${this.renderSection(Category.ERROR)}
       ${this.renderSection(Category.WARNING)}
-      ${this.renderSection(Category.INFO)} ${this.renderSuccess()}
+      ${this.renderSection(Category.INFO)} ${this.renderSection('SUCCESS')}
     `;
   }
 
@@ -384,36 +407,62 @@
     return html`<div class="noCompleted">${text}</div>`;
   }
 
-  renderSection(category: Category) {
+  renderSection(category: Category | 'SUCCESS') {
     const catString = category.toString().toLowerCase();
-    const runs = this.runs.filter(r =>
-      (r.results ?? []).some(res => res.category === category)
-    );
+    let runs = this.runs;
+    if (category === 'SUCCESS') {
+      runs = runs
+        .filter(hasCompletedWithoutResults)
+        .filter(r => this.filterRegExp.test(r.checkName));
+    } else {
+      runs = runs.filter(r =>
+        (r.results ?? []).some(res => res.category === category)
+      );
+    }
     if (runs.length === 0) return;
+    const expanded = this.isSectionExpanded.get(category) ?? true;
+    const expandedClass = expanded ? 'expanded' : 'collapsed';
+    const icon = expanded ? 'gr-icons:expand-more' : 'gr-icons:expand-less';
     return html`
-      <h3 class="categoryHeader heading-3">
-        <iron-icon
-          icon="gr-icons:${iconForCategory(category)}"
-          class="${catString}"
-        ></iron-icon>
-        ${catString}
-      </h3>
-      <table class="resultsTable">
-        <thead>
-          <tr class="headerRow">
-            <th class="iconCol"></th>
-            <th class="nameCol">Run</th>
-            <th class="summaryCol">Summary</th>
-            <th class="expanderCol"></th>
-          </tr>
-        </thead>
-        <tbody>
-          ${runs.map(run => this.renderRun(category, run))}
-        </tbody>
-      </table>
+      <div class="${expandedClass}">
+        <h3
+          class="categoryHeader heading-3"
+          @click="${() => this.toggleExpanded(category)}"
+        >
+          <iron-icon class="expandIcon" icon="${icon}"></iron-icon>
+          <iron-icon
+            icon="gr-icons:${iconForCategory(category)}"
+            class="statusIcon ${catString}"
+          ></iron-icon>
+          ${catString}
+        </h3>
+        <table class="resultsTable">
+          <thead>
+            <tr class="headerRow">
+              <th class="iconCol"></th>
+              <th class="nameCol">Run</th>
+              <th class="summaryCol">Summary</th>
+              <th class="expanderCol"></th>
+            </tr>
+          </thead>
+          <tbody>
+            ${runs.map(run =>
+              category === 'SUCCESS'
+                ? this.renderSuccessfulRun(run)
+                : this.renderRun(category, run)
+            )}
+          </tbody>
+        </table>
+      </div>
     `;
   }
 
+  toggleExpanded(category: Category | 'SUCCESS') {
+    const expanded = this.isSectionExpanded.get(category) ?? true;
+    this.isSectionExpanded.set(category, !expanded);
+    this.requestUpdate();
+  }
+
   renderRun(category: Category, run: CheckRun) {
     return html`${run.results
       ?.filter(result => result.category === category)
@@ -428,38 +477,30 @@
       )}`;
   }
 
-  renderSuccess() {
-    const runs = this.runs
-      .filter(hasCompletedWithoutResults)
-      .filter(r => this.filterRegExp.test(r.checkName));
-    if (runs.length === 0) return;
-    return html`
-      <h3 class="categoryHeader heading-3">
-        <iron-icon
-          icon="gr-icons:check-circle-outline"
-          class="success"
-        ></iron-icon>
-        Success
-      </h3>
-      <table class="resultsTable">
-        <tr class="headerRow">
-          <th class="iconCol"></th>
-          <th class="nameCol">Run</th>
-          <th class="summaryCol">Summary</th>
-          <th class="expanderCol"></th>
-        </tr>
-        ${runs.map(run => this.renderSuccessfulRun(run))}
-      </table>
-    `;
-  }
-
   renderSuccessfulRun(run: CheckRun) {
     const adaptedRun: RunResult = {
       category: Category.INFO, // will not be used, but is required
       summary: run.statusDescription ?? '',
-      message: 'Completed without results.',
       ...run,
     };
+    if (!run.statusDescription) {
+      const start = run.scheduledTimestamp ?? run.startedTimestamp;
+      const end = run.finishedTimestamp;
+      let duration = '';
+      if (start && end) {
+        duration = ` in ${durationString(start, end, true)}`;
+      }
+      adaptedRun.message = `Completed without results${duration}.`;
+    }
+    if (run.statusLink) {
+      adaptedRun.links = [
+        {
+          url: run.statusLink,
+          primary: true,
+          icon: LinkIcon.EXTERNAL,
+        },
+      ];
+    }
     return html`<gr-result-row .result="${adaptedRun}"></gr-result-row>`;
   }
 }
diff --git a/polygerrit-ui/app/elements/checks/gr-checks-runs.ts b/polygerrit-ui/app/elements/checks/gr-checks-runs.ts
index 71ad041..31f17724 100644
--- a/polygerrit-ui/app/elements/checks/gr-checks-runs.ts
+++ b/polygerrit-ui/app/elements/checks/gr-checks-runs.ts
@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import {html} from 'lit-html';
+import {html, nothing} from 'lit-html';
 import {classMap} from 'lit-html/directives/class-map';
 import {
   css,
@@ -29,8 +29,10 @@
 import {
   compareByWorstCategory,
   fireActionTriggered,
+  iconForCategory,
   iconForRun,
   primaryRunAction,
+  worstCategory,
 } from '../../services/checks/checks-util';
 import {
   allRuns$,
@@ -41,7 +43,7 @@
   fakeRun4,
   updateStateSetResults,
 } from '../../services/checks/checks-model';
-import {assertIsDefined, toggleSetMembership} from '../../utils/common-util';
+import {assertIsDefined} from '../../utils/common-util';
 import {whenVisible} from '../../utils/dom-util';
 
 export interface RunSelectedEventDetail {
@@ -111,16 +113,19 @@
         .chip.placeholder {
           border-left: var(--thick-border) solid var(--border-color);
         }
-        .chip.error iron-icon {
+        .chip.placeholder iron-icon {
+          display: none;
+        }
+        iron-icon.error {
           color: var(--error-foreground);
         }
-        .chip.warning iron-icon {
+        iron-icon.warning {
           color: var(--warning-foreground);
         }
-        .chip.info-outline iron-icon {
+        iron-icon.info-outline {
           color: var(--info-foreground);
         }
-        .chip.check-circle-outline iron-icon {
+        iron-icon.check-circle-outline {
           color: var(--success-foreground);
         }
         /* Additional 'div' for increased specificity. */
@@ -195,7 +200,8 @@
     return html`
       <div @click="${this.handleChipClick}" class="${classMap(classes)}">
         <div class="left">
-          <iron-icon icon="gr-icons:${icon}"></iron-icon>
+          <iron-icon class="${icon}" icon="gr-icons:${icon}"></iron-icon>
+          ${this.renderAdditionalIcon()}
           <span class="name">${this.run.checkName}</span>
         </div>
         <div class="right">
@@ -212,6 +218,20 @@
     `;
   }
 
+  /**
+   * For RUNNING we also want to render an icon representing the worst result
+   * that has been reported until now - if there are any results already.
+   */
+  renderAdditionalIcon() {
+    if (this.run.status !== RunStatus.RUNNING) return nothing;
+    const category = worstCategory(this.run);
+    if (!category) return nothing;
+    const icon = iconForCategory(category);
+    return html`
+      <iron-icon class="${icon}" icon="gr-icons:${icon}"></iron-icon>
+    `;
+  }
+
   private handleChipClick(e: MouseEvent) {
     e.stopPropagation();
     e.preventDefault();
@@ -236,7 +256,10 @@
   @property()
   runs: CheckRun[] = [];
 
-  private selectedRuns = new Set<string>();
+  @property()
+  selectedRuns: string[] = [];
+
+  private isSectionExpanded = new Map<RunStatus, boolean>();
 
   constructor() {
     super();
@@ -251,9 +274,24 @@
           display: block;
           padding: var(--spacing-xl);
         }
-        .statusHeader {
+        .expandIcon {
+          width: var(--line-height-h3);
+          height: var(--line-height-h3);
+        }
+        .sectionHeader {
           padding-top: var(--spacing-l);
           text-transform: capitalize;
+          cursor: default;
+        }
+        .sectionHeader h3 {
+          display: inline-block;
+        }
+        .collapsed .sectionRuns {
+          display: none;
+        }
+        .collapsed {
+          border-bottom: 1px solid var(--border-color);
+          padding-bottom: var(--spacing-m);
         }
         input#filterInput {
           margin-top: var(--spacing-s);
@@ -344,29 +382,40 @@
       .filter(r => this.filterRegExp.test(r.checkName))
       .sort(compareByWorstCategory);
     if (runs.length === 0) return;
+    const expanded = this.isSectionExpanded.get(status) ?? true;
+    const expandedClass = expanded ? 'expanded' : 'collapsed';
+    const icon = expanded ? 'gr-icons:expand-more' : 'gr-icons:expand-less';
     return html`
-      <div class="${status.toLowerCase()}">
-        <h3 class="statusHeader heading-3">${status.toLowerCase()}</h3>
-        ${runs.map(run => this.renderRun(run))}
+      <div class="${status.toLowerCase()} ${expandedClass}">
+        <div
+          class="sectionHeader"
+          @click="${() => this.toggleExpanded(status)}"
+        >
+          <iron-icon class="expandIcon" icon="${icon}"></iron-icon>
+          <h3 class="heading-3">${status.toLowerCase()}</h3>
+        </div>
+        <div class="sectionRuns">
+          ${runs.map(run => this.renderRun(run))}
+        </div>
       </div>
     `;
   }
 
+  toggleExpanded(status: RunStatus) {
+    const expanded = this.isSectionExpanded.get(status) ?? true;
+    this.isSectionExpanded.set(status, !expanded);
+    this.requestUpdate();
+  }
+
   renderRun(run: CheckRun) {
-    const selected = this.selectedRuns.has(run.checkName);
-    const deselected = !selected && this.selectedRuns.size > 0;
+    const selected = this.selectedRuns.includes(run.checkName);
+    const deselected = !selected && this.selectedRuns.length > 0;
     return html`<gr-checks-run
       .run="${run}"
       .selected="${selected}"
       .deselected="${deselected}"
-      @run-selected="${this.handleRunSelected}"
     ></gr-checks-run>`;
   }
-
-  handleRunSelected(e: RunSelectedEvent) {
-    toggleSetMembership(this.selectedRuns, e.detail.checkName);
-    this.requestUpdate();
-  }
 }
 
 declare global {
diff --git a/polygerrit-ui/app/elements/checks/gr-checks-tab.ts b/polygerrit-ui/app/elements/checks/gr-checks-tab.ts
index 0ce81ed..c072f2c 100644
--- a/polygerrit-ui/app/elements/checks/gr-checks-tab.ts
+++ b/polygerrit-ui/app/elements/checks/gr-checks-tab.ts
@@ -15,28 +15,42 @@
  * limitations under the License.
  */
 import {html} from 'lit-html';
-import {css, customElement, property} from 'lit-element';
+import {
+  css,
+  customElement,
+  internalProperty,
+  property,
+  PropertyValues,
+} from 'lit-element';
 import {GrLitElement} from '../lit/gr-lit-element';
 import {Action, CheckResult, CheckRun} from '../../api/checks';
 import {
   allActions$,
   allResults$,
   allRuns$,
+  checksPatchsetNumber$,
+  someProvidersAreLoading$,
 } from '../../services/checks/checks-model';
 import './gr-checks-runs';
 import './gr-checks-results';
 import {sharedStyles} from '../../styles/shared-styles';
-import {changeNum$, currentPatchNum$} from '../../services/change/change-model';
-import {NumericChangeId, PatchSetNum} from '../../types/common';
+import {changeNum$, latestPatchNum$} from '../../services/change/change-model';
+import {NumericChangeId, PatchSetNumber} from '../../types/common';
 import {
   ActionTriggeredEvent,
   fireActionTriggered,
 } from '../../services/checks/checks-util';
 import {
+  assertIsDefined,
+  check,
   checkRequiredProperty,
-  toggleSetMembership,
 } from '../../utils/common-util';
 import {RunSelectedEvent} from './gr-checks-runs';
+import {ChecksTabState} from '../../types/events';
+import {fireAlert} from '../../utils/event-util';
+import {appContext} from '../../services/app-context';
+import {from, timer} from 'rxjs';
+import {takeUntil} from 'rxjs/operators';
 
 /**
  * The "Checks" tab on the Gerrit change page. Gets its data from plugins that
@@ -52,20 +66,34 @@
   actions: Action[] = [];
 
   @property()
-  currentPatchNum: PatchSetNum | undefined = undefined;
+  tabState?: ChecksTabState;
+
+  @property()
+  checksPatchsetNumber: PatchSetNumber | undefined = undefined;
+
+  @property()
+  latestPatchsetNumber: PatchSetNumber | undefined = undefined;
 
   @property()
   changeNum: NumericChangeId | undefined = undefined;
 
-  private selectedRuns = new Set<string>();
+  @property()
+  someProvidersAreLoading = false;
+
+  @internalProperty()
+  selectedRuns: string[] = [];
+
+  private readonly checksService = appContext.checksService;
 
   constructor() {
     super();
     this.subscribe('runs', allRuns$);
     this.subscribe('actions', allActions$);
     this.subscribe('results', allResults$);
-    this.subscribe('currentPatchNum', currentPatchNum$);
+    this.subscribe('checksPatchsetNumber', checksPatchsetNumber$);
+    this.subscribe('latestPatchsetNumber', latestPatchNum$);
     this.subscribe('changeNum', changeNum$);
+    this.subscribe('someProvidersAreLoading', someProvidersAreLoading$);
 
     this.addEventListener('action-triggered', (e: ActionTriggeredEvent) =>
       this.handleActionTriggered(e.detail.action, e.detail.run)
@@ -105,22 +133,20 @@
   }
 
   render() {
-    const ps = `Patchset ${this.currentPatchNum} (Latest)`;
     const filteredRuns = this.runs.filter(
-      r => this.selectedRuns.size === 0 || this.selectedRuns.has(r.checkName)
+      r =>
+        this.selectedRuns.length === 0 ||
+        this.selectedRuns.includes(r.checkName)
     );
     return html`
       <div class="header">
         <div class="left">
           <gr-dropdown-list
-            value="${ps}"
-            .items="${[
-              {
-                value: `${ps}`,
-                text: `${ps}`,
-              },
-            ]}"
+            value="${this.checksPatchsetNumber}"
+            .items="${this.createPatchsetDropdownItems()}"
+            @value-change="${this.onPatchsetSelected}"
           ></gr-dropdown-list>
+          <span ?hidden="${!this.someProvidersAreLoading}">Loading...</span>
         </div>
         <div class="right">
           ${this.actions.map(this.renderAction)}
@@ -130,6 +156,7 @@
         <gr-checks-runs
           class="runs"
           .runs="${this.runs}"
+          .selectedRuns="${this.selectedRuns}"
           @run-selected="${this.handleRunSelected}"
         ></gr-checks-runs>
         <gr-checks-results
@@ -140,6 +167,35 @@
     `;
   }
 
+  private onPatchsetSelected(e: CustomEvent<{value: string}>) {
+    const patchset = Number(e.detail.value);
+    check(!isNaN(patchset), 'selected patchset must be a number');
+    this.checksService.setPatchset(patchset as PatchSetNumber);
+  }
+
+  private createPatchsetDropdownItems() {
+    if (!this.latestPatchsetNumber) return [];
+    return Array.from(Array(this.latestPatchsetNumber), (_, i) => {
+      assertIsDefined(this.latestPatchsetNumber, 'latestPatchsetNumber');
+      const index = this.latestPatchsetNumber - i;
+      const postfix = index === this.latestPatchsetNumber ? ' (latest)' : '';
+      return {
+        value: `${index}`,
+        text: `Patchset ${index}${postfix}`,
+      };
+    });
+  }
+
+  protected updated(changedProperties: PropertyValues) {
+    super.updated(changedProperties);
+    if (changedProperties.has('tabState')) {
+      const check = this.tabState?.checkName;
+      if (check) {
+        this.selectedRuns = [check];
+      }
+    }
+  }
+
   renderAction(action: Action) {
     return html`<gr-checks-top-level-action
       .action="${action}"
@@ -148,23 +204,46 @@
 
   handleActionTriggered(action: Action, run?: CheckRun) {
     if (!this.changeNum) return;
-    if (!this.currentPatchNum) return;
-    // TODO(brohlfs): The callback is supposed to be returning a promise.
-    // A toast should be displayed until the promise completes. And then the
-    // data should be updated.
-    action.callback(
+    if (!this.checksPatchsetNumber) return;
+    const promise = action.callback(
       this.changeNum,
-      this.currentPatchNum as number,
+      this.checksPatchsetNumber,
       run?.attempt,
       run?.externalId,
       run?.checkName,
       action.name
     );
+    // Plugins *should* return a promise, but you never know ...
+    if (promise?.then) {
+      const prefix = `Triggering action '${action.name}'`;
+      fireAlert(this, `${prefix} ...`);
+      from(promise)
+        // If the action takes longer than 5 seconds, then most likely the
+        // user is either not interested or the result not relevant anymore.
+        .pipe(takeUntil(timer(5000)))
+        .subscribe(result => {
+          if (result.errorMessage) {
+            fireAlert(this, `${prefix} failed with ${result.errorMessage}.`);
+          } else {
+            fireAlert(this, `${prefix} successful.`);
+            this.checksService.reloadForCheck(run?.checkName);
+          }
+        });
+    } else {
+      fireAlert(this, `Action '${action.name}' triggered.`);
+    }
   }
 
   handleRunSelected(e: RunSelectedEvent) {
-    toggleSetMembership(this.selectedRuns, e.detail.checkName);
-    this.requestUpdate();
+    this.toggleSelected(e.detail.checkName);
+  }
+
+  toggleSelected(checkName: string) {
+    if (this.selectedRuns.includes(checkName)) {
+      this.selectedRuns = this.selectedRuns.filter(r => r !== checkName);
+    } else {
+      this.selectedRuns = [...this.selectedRuns, checkName];
+    }
   }
 }
 
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
index b43b3b0..bed07a6 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.ts
@@ -304,7 +304,7 @@
         if (!config) {
           throw new Error('getConfig returned undefined');
         }
-        this._retreiveFeedbackURL(config);
+        this._retrieveFeedbackURL(config);
         this._retrieveRegisterURL(config);
         return getDocsBaseUrl(config, this.restApiService);
       })
@@ -325,7 +325,7 @@
     });
   }
 
-  _retreiveFeedbackURL(config: ServerInfo) {
+  _retrieveFeedbackURL(config: ServerInfo) {
     if (config.gerrit?.report_bug_url) {
       this._feedbackURL = config.gerrit.report_bug_url;
     }
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_test.ts b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_test.ts
index 7430cc0..d9c43d6 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_test.ts
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_test.ts
@@ -488,7 +488,7 @@
         report_bug_url: url,
       },
     };
-    element._retreiveFeedbackURL(config);
+    element._retrieveFeedbackURL(config);
     await flush();
 
     assert.equal(element._feedbackURL, url);
diff --git a/polygerrit-ui/app/elements/core/gr-navigation/gr-navigation.ts b/polygerrit-ui/app/elements/core/gr-navigation/gr-navigation.ts
index f2ee838..632ce4c 100644
--- a/polygerrit-ui/app/elements/core/gr-navigation/gr-navigation.ts
+++ b/polygerrit-ui/app/elements/core/gr-navigation/gr-navigation.ts
@@ -249,7 +249,7 @@
 
 export interface GenerateUrlChangeViewParameters {
   view: GerritView.CHANGE;
-  // TODO(TS): NumericChangeId - not sure about it, may be it can be removeds
+  // TODO(TS): NumericChangeId - not sure about it, may be it can be removed
   changeNum: NumericChangeId;
   project: RepoName;
   patchNum?: PatchSetNum;
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
index 3a76112..676ef7b 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router.ts
@@ -308,15 +308,6 @@
 
   private readonly restApiService = appContext.restApiService;
 
-  private readonly changeService = appContext.changeService;
-
-  constructor() {
-    super();
-    // TODO: This is just an artificical dependdency such that the service is
-    // instantiated and its observables subscribed. Remove this later.
-    this.changeService.dontDoAnything();
-  }
-
   start() {
     if (!this._app) {
       return;
diff --git a/polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.ts b/polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.ts
index 43f8a2b..32e0083 100644
--- a/polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.ts
+++ b/polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.ts
@@ -40,10 +40,12 @@
 // Possible static search options for auto complete, without negations.
 const SEARCH_OPERATORS: ReadonlyArray<string> = [
   'added:',
+  'after:',
   'age:',
   'age:1week', // Give an example age
   'assignee:',
   'author:',
+  'before:',
   'branch:',
   'bug:',
   'cc:',
@@ -77,6 +79,7 @@
   'is:assigned',
   'is:closed',
   'is:ignored',
+  'is:merge',
   'is:merged',
   'is:open',
   'is:owner',
@@ -88,11 +91,14 @@
   'is:watched',
   'is:wip',
   'label:',
+  'mergedafter:',
+  'mergedbefore:',
   'message:',
   'onlyexts:',
   'onlyextensions:',
   'owner:',
   'ownerin:',
+  'parentof:',
   'parentproject:',
   'project:',
   'projects:',
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.ts b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.ts
index 829038b..4943298 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.ts
@@ -33,7 +33,7 @@
 
 /**
  * In JS, unicode code points above 0xFFFF occupy two elements of a string.
- * For example '𐀏'.length is 2. An occurence of such a code point is called a
+ * For example '𐀏'.length is 2. An occurrence of such a code point is called a
  * surrogate pair.
  *
  * This regex segments a string along tabs ('\t') and surrogate pairs, since
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-overview-image.ts b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-overview-image.ts
new file mode 100644
index 0000000..42268e9
--- /dev/null
+++ b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-overview-image.ts
@@ -0,0 +1,304 @@
+/**
+ * @license
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import {
+  css,
+  customElement,
+  html,
+  internalProperty,
+  LitElement,
+  property,
+  PropertyValues,
+  query,
+} from 'lit-element';
+import {StyleInfo, styleMap} from 'lit-html/directives/style-map';
+
+import {Dimensions, fitToFrame, Point, Rect} from './util';
+
+/**
+ * Displays a scaled-down version of an image with a draggable frame for
+ * choosing a portion of the image to be magnified by other components.
+ *
+ * Slotted content can be arbitrary elements, but should be limited to images or
+ * stacks of image-like elements (e.g. for overlays) with limited interactivity,
+ * to prevent confusion, as the component only captures a limited set of events.
+ * Slotted content is scaled to fit the bounds of the component, with
+ * letterboxing if aspect ratios differ. For slotted content smaller than the
+ * component, it will cap the scale at 1x and also apply letterboxing.
+ */
+@customElement('gr-overview-image')
+export class GrOverviewImage extends LitElement {
+  @property({type: Object})
+  frameRect: Rect = {origin: {x: 0, y: 0}, dimensions: {width: 0, height: 0}};
+
+  @internalProperty() protected contentStyle: StyleInfo = {};
+
+  @internalProperty() protected contentTransformStyle: StyleInfo = {};
+
+  @internalProperty() protected frameStyle: StyleInfo = {};
+
+  @internalProperty() protected overlayStyle: StyleInfo = {};
+
+  @internalProperty() protected dragging = false;
+
+  @query('.content-box') protected contentBox!: HTMLDivElement;
+
+  @query('.content') protected content!: HTMLDivElement;
+
+  @query('.content-transform') protected contentTransform!: HTMLDivElement;
+
+  @query('.frame') protected frame!: HTMLDivElement;
+
+  private contentBounds: Dimensions = {width: 0, height: 0};
+
+  private imageBounds: Dimensions = {width: 0, height: 0};
+
+  private scale = 1;
+
+  // When grabbing the frame to drag it around, this stores the offset of the
+  // cursor from the center of the frame at the start of the drag.
+  private grabOffset: Point = {x: 0, y: 0};
+
+  private readonly resizeObserver = new ResizeObserver(
+    (entries: ResizeObserverEntry[]) => {
+      for (const entry of entries) {
+        if (entry.target === this.contentBox) {
+          this.contentBounds = {
+            width: entry.contentRect.width,
+            height: entry.contentRect.height,
+          };
+        }
+        if (entry.target === this.contentTransform) {
+          this.imageBounds = {
+            width: entry.contentRect.width,
+            height: entry.contentRect.height,
+          };
+        }
+        this.updateScale();
+      }
+    }
+  );
+
+  static styles = css`
+    :host {
+      --overview-image-background-color: #000;
+      --overview-image-frame-color: #f00;
+      display: flex;
+    }
+    * {
+      box-sizing: border-box;
+    }
+    ::slotted(*) {
+      display: block;
+    }
+    .content-box {
+      border: 1px solid var(--overview-image-background-color);
+      background-color: var(--overview-iamge-background-color);
+      width: 100%;
+      position: relative;
+    }
+    .content {
+      position: absolute;
+      cursor: pointer;
+    }
+    .content-transform {
+      position: absolute;
+      transform-origin: top left;
+      will-change: transform;
+    }
+    .frame {
+      border: 1px solid var(--overview-image-frame-color);
+      position: absolute;
+      will-change: transform;
+    }
+    .overlay {
+      position: absolute;
+      z-index: 10000;
+      cursor: grabbing;
+    }
+  `;
+
+  render() {
+    return html`
+      <div class="content-box">
+        <div
+          class="content"
+          style="${styleMap({
+            ...this.contentStyle,
+          })}"
+          @mousemove="${this.maybeDragFrame}"
+          @mousedown=${this.clickOverview}
+          @mouseup="${this.releaseFrame}"
+        >
+          <div
+            class="content-transform"
+            style="${styleMap(this.contentTransformStyle)}"
+          >
+            <slot></slot>
+          </div>
+          <div
+            class="frame"
+            style="${styleMap({
+              ...this.frameStyle,
+              cursor: this.dragging ? 'grabbing' : 'grab',
+            })}"
+            @mousedown="${this.grabFrame}"
+          ></div>
+        </div>
+        <div
+          class="overlay"
+          style="${styleMap({
+            ...this.overlayStyle,
+            display: this.dragging ? 'block' : 'none',
+          })}"
+          @mousemove="${this.overlayMouseMove}"
+          @mouseleave="${this.releaseFrame}"
+          @mouseup="${this.releaseFrame}"
+        ></div>
+      </div>
+    `;
+  }
+
+  firstUpdated() {
+    this.resizeObserver.observe(this.contentBox);
+    this.resizeObserver.observe(this.contentTransform);
+  }
+
+  updated(changedProperties: PropertyValues) {
+    if (changedProperties.has('frameRect')) {
+      this.updateFrameStyle();
+    }
+  }
+
+  clickOverview(event: MouseEvent) {
+    event.preventDefault();
+
+    this.updateOverlaySize();
+
+    this.dragging = true;
+    const rect = this.content.getBoundingClientRect();
+    this.notifyNewCenter({
+      x: (event.clientX - rect.left) / this.scale,
+      y: (event.clientY - rect.top) / this.scale,
+    });
+  }
+
+  grabFrame(event: MouseEvent) {
+    event.preventDefault();
+    // Do not bubble up into clickOverview().
+    event.stopPropagation();
+
+    this.updateOverlaySize();
+
+    this.dragging = true;
+    const rect = this.frame.getBoundingClientRect();
+    const frameCenterX = rect.x + rect.width / 2;
+    const frameCenterY = rect.y + rect.height / 2;
+    this.grabOffset = {
+      x: event.clientX - frameCenterX,
+      y: event.clientY - frameCenterY,
+    };
+  }
+
+  maybeDragFrame(event: MouseEvent) {
+    event.preventDefault();
+    if (!this.dragging) return;
+    const rect = this.content.getBoundingClientRect();
+    const center = {
+      x: (event.clientX - rect.left - this.grabOffset.x) / this.scale,
+      y: (event.clientY - rect.top - this.grabOffset.y) / this.scale,
+    };
+    this.notifyNewCenter(center);
+  }
+
+  releaseFrame(event: MouseEvent) {
+    event.preventDefault();
+    this.dragging = false;
+    this.grabOffset = {x: 0, y: 0};
+  }
+
+  overlayMouseMove(event: MouseEvent) {
+    event.preventDefault();
+    this.maybeDragFrame(event);
+  }
+
+  private updateScale() {
+    const fitted = fitToFrame(this.imageBounds, this.contentBounds);
+    this.scale = fitted.scale;
+
+    this.contentStyle = {
+      ...this.contentStyle,
+      top: `${fitted.top}px`,
+      left: `${fitted.left}px`,
+      width: `${fitted.width}px`,
+      height: `${fitted.height}px`,
+    };
+
+    this.contentTransformStyle = {
+      transform: `scale(${this.scale})`,
+    };
+
+    this.updateFrameStyle();
+  }
+
+  private updateFrameStyle() {
+    const x = this.frameRect.origin.x * this.scale;
+    const y = this.frameRect.origin.y * this.scale;
+    const width = this.frameRect.dimensions.width * this.scale;
+    const height = this.frameRect.dimensions.height * this.scale;
+    this.frameStyle = {
+      ...this.frameStyle,
+      transform: `translate(${x}px, ${y}px)`,
+      width: `${width}px`,
+      height: `${height}px`,
+    };
+  }
+
+  private updateOverlaySize() {
+    const rect = this.contentBox.getBoundingClientRect();
+    // Create a whole-page overlay to capture mouse events, so that the drag
+    // interaction continues until the user releases the mouse button. Since
+    // innerWidth and innerHeight include scrollbars, we subtract 20 pixels each
+    // to prevent the overlay from extending offscreen under any existing
+    // scrollbar and causing the scrollbar for the other dimension to show up
+    // unnecessarily.
+    const width = window.innerWidth - 20;
+    const height = window.innerHeight - 20;
+    this.overlayStyle = {
+      ...this.overlayStyle,
+      top: `-${rect.top + 1}px`,
+      left: `-${rect.left + 1}px`,
+      width: `${width}px`,
+      height: `${height}px`,
+    };
+  }
+
+  private notifyNewCenter(center: Point) {
+    this.dispatchEvent(
+      new CustomEvent('center-updated', {
+        detail: {...center},
+        bubbles: true,
+        composed: true,
+      })
+    );
+  }
+}
+
+declare global {
+  interface HTMLElementTagNameMap {
+    'gr-overview-image': GrOverviewImage;
+  }
+}
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-zoomed-image.ts b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-zoomed-image.ts
new file mode 100644
index 0000000..a14a9cc
--- /dev/null
+++ b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/gr-zoomed-image.ts
@@ -0,0 +1,95 @@
+/**
+ * @license
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import {
+  css,
+  customElement,
+  html,
+  internalProperty,
+  LitElement,
+  property,
+  PropertyValues,
+} from 'lit-element';
+import {StyleInfo, styleMap} from 'lit-html/directives/style-map';
+import {Rect} from './util';
+
+/**
+ * Displays its slotted content at a given scale, centered over a given point,
+ * while ensuring the content always fills the container. The content does not
+ * have to be a single image, it can be arbitrary HTML. To prevent user
+ * confusion, it should ideally be image-like, i.e. have limited or no
+ * interactivity, as the component does not prevent events or focus from
+ * reaching the slotted content.
+ */
+@customElement('gr-zoomed-image')
+export class GrZoomedImage extends LitElement {
+  @property({type: Number}) scale = 1;
+
+  @property({type: Object})
+  frameRect: Rect = {origin: {x: 0, y: 0}, dimensions: {width: 0, height: 0}};
+
+  @internalProperty() protected imageStyles: StyleInfo = {};
+
+  static styles = css`
+    :host {
+      display: block;
+    }
+    ::slotted(*) {
+      display: block;
+    }
+    #clip {
+      position: relative;
+      width: 100%;
+      height: 100%;
+      overflow: hidden;
+    }
+    #transform {
+      position: absolute;
+      transform-origin: top left;
+      will-change: transform;
+    }
+  `;
+
+  render() {
+    return html`
+      <div id="clip">
+        <div id="transform" style="${styleMap(this.imageStyles)}">
+          <slot></slot>
+        </div>
+      </div>
+    `;
+  }
+
+  updated(changedProperties: PropertyValues) {
+    if (changedProperties.has('scale') || changedProperties.has('frameRect')) {
+      this.updateImageStyles();
+    }
+  }
+
+  private updateImageStyles() {
+    const {x, y} = this.frameRect.origin;
+    this.imageStyles = {
+      'image-rendering': this.scale >= 1 ? 'pixelated' : 'auto',
+      transform: `translate(${-x}px, ${-y}px) scale(${this.scale})`,
+    };
+  }
+}
+
+declare global {
+  interface HTMLElementTagNameMap {
+    'gr-zoomed-image': GrZoomedImage;
+  }
+}
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util.ts b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util.ts
new file mode 100644
index 0000000..b42eea9
--- /dev/null
+++ b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util.ts
@@ -0,0 +1,236 @@
+/**
+ * @license
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export interface Point {
+  x: number;
+  y: number;
+}
+
+export interface Dimensions {
+  width: number;
+  height: number;
+}
+
+export interface Rect {
+  origin: Point;
+  dimensions: Dimensions;
+}
+
+export interface FittedContent {
+  top: number;
+  left: number;
+  width: number;
+  height: number;
+  scale: number;
+}
+
+function clamp(value: number, min: number, max: number) {
+  return Math.max(min, Math.min(value, max));
+}
+
+/**
+ * Fits content of the given dimensions into the given frame, maintaining the
+ * aspect ratio of the content and applying letterboxing / pillarboxing as
+ * needed.
+ */
+export function fitToFrame(
+  content: Dimensions,
+  frame: Dimensions
+): FittedContent {
+  const contentAspectRatio = content.width / content.height;
+  const frameAspectRatio = frame.width / frame.height;
+  // If the content is wider than the frame, it will be letterboxed, otherwise
+  // it will be pillarboxed. When letterboxed, content and frame width will
+  // match exactly, when pillarboxed, content and frame height will match
+  // exactly.
+  const isLetterboxed = contentAspectRatio > frameAspectRatio;
+  let width: number;
+  let height: number;
+  if (isLetterboxed) {
+    width = Math.min(frame.width, content.width);
+    height = content.height * (width / content.width);
+  } else {
+    height = Math.min(frame.height, content.height);
+    width = content.width * (height / content.height);
+  }
+  const top = (frame.height - height) / 2;
+  const left = (frame.width - width) / 2;
+  const scale = width / content.width;
+  return {top, left, width, height, scale};
+}
+
+function ensureInBounds(part: Rect, bounds: Dimensions): Rect {
+  const x =
+    part.dimensions.width <= bounds.width
+      ? clamp(part.origin.x, 0, bounds.width - part.dimensions.width)
+      : (bounds.width - part.dimensions.width) / 2;
+  const y =
+    part.dimensions.height <= bounds.height
+      ? clamp(part.origin.y, 0, bounds.height - part.dimensions.height)
+      : (bounds.height - part.dimensions.height) / 2;
+  return {origin: {x, y}, dimensions: part.dimensions};
+}
+
+/**
+ * Maintains a given frame inside given bounds, adjusting requested positions
+ * for the frame as needed. This supports the non-destructive application of a
+ * scaling factor, so that e.g. the magnification of an image can be changed
+ * easily while keeping the frame centered over the same spot. Changing bounds
+ * or frame size also keeps the frame position when possible.
+ */
+export class FrameConstrainer {
+  private center: Point = {x: 0, y: 0};
+
+  private frameSize: Dimensions = {width: 0, height: 0};
+
+  private bounds: Dimensions = {width: 0, height: 0};
+
+  private scale = 1;
+
+  private unscaledFrame: Rect = {
+    origin: {x: 0, y: 0},
+    dimensions: {width: 0, height: 0},
+  };
+
+  private scaledFrame: Rect = {
+    origin: {x: 0, y: 0},
+    dimensions: {width: 0, height: 0},
+  };
+
+  getCenter(): Point {
+    return {...this.center};
+  }
+
+  /**
+   * Returns the frame at its original size, positioned within the given bounds
+   * at the given scale; its origin will be in scaled bounds coordinates.
+   *
+   * Ex: for given bounds 100x50 and frame size 30x20, centered over (50, 25),
+   * all at 1x scale, when setting scale to 2, this will return a frame of size
+   * 30x20, centered over (100, 50), within bounds 200x100.
+   *
+   * Useful for positioning a viewport of fixed size over a magnified image.
+   */
+  getUnscaledFrame(): Rect {
+    return {
+      origin: {...this.unscaledFrame.origin},
+      dimensions: {...this.unscaledFrame.dimensions},
+    };
+  }
+
+  /**
+   * Returns the scaled down frame–a scale of 2 will result in frame dimensions
+   * being halved—position within the given bounds at 1x scale; its origin will
+   * be in unscaled bounds coordinates.
+   *
+   * Ex: for given bounds 100x50 and frame size 30x20, centered over (50, 25),
+   * all at 1x scale, when setting scale to 2, this will return a frame of size
+   * 15x10, centered over (50, 25), within bounds 100x50.
+   *
+   * Useful for highlighting the magnified portion of an image as determined by
+   * getUnscaledFrame() in an overview image of fixed size.
+   */
+  getScaledFrame(): Rect {
+    return {
+      origin: {...this.scaledFrame.origin},
+      dimensions: {...this.scaledFrame.dimensions},
+    };
+  }
+
+  /**
+   * Requests the frame to be centered over the given point, in unscaled bounds
+   * coordinates. This will keep the frame within the given bounds, also when
+   * requesting a center point fully outside the given bounds.
+   */
+  requestCenter(center: Point) {
+    this.center = {...center};
+
+    this.ensureFrameInBounds();
+  }
+
+  /**
+   * Sets the frame size, while keeping the frame within the given bounds, and
+   * maintaining the current center if possible.
+   */
+  setFrameSize(frameSize: Dimensions) {
+    if (frameSize.width <= 0 || frameSize.height <= 0) return;
+    this.frameSize = {...frameSize};
+
+    this.ensureFrameInBounds();
+  }
+
+  /**
+   * Sets the bounds, while keeping the frame within them, and maintaining the
+   * current center if possible.
+   */
+  setBounds(bounds: Dimensions) {
+    if (bounds.width <= 0 || bounds.height <= 0) return;
+    this.bounds = {...bounds};
+
+    this.ensureFrameInBounds();
+  }
+
+  /**
+   * Sets the applied scale, while keeping the frame within the given bounds,
+   * and maintaining the current center if possible (both relevant moving from
+   * a larger scale to a smaller scale).
+   */
+  setScale(scale: number) {
+    if (!scale || scale <= 0) return;
+    this.scale = scale;
+
+    this.ensureFrameInBounds();
+  }
+
+  private ensureFrameInBounds() {
+    const scaledCenter = {
+      x: this.center.x * this.scale,
+      y: this.center.y * this.scale,
+    };
+    const scaledBounds = {
+      width: this.bounds.width * this.scale,
+      height: this.bounds.height * this.scale,
+    };
+    const scaledFrameSize = {
+      width: this.frameSize.width / this.scale,
+      height: this.frameSize.height / this.scale,
+    };
+
+    const requestedUnscaledFrame = {
+      origin: {
+        x: scaledCenter.x - this.frameSize.width / 2,
+        y: scaledCenter.y - this.frameSize.height / 2,
+      },
+      dimensions: this.frameSize,
+    };
+    const requestedScaledFrame = {
+      origin: {
+        x: this.center.x - scaledFrameSize.width / 2,
+        y: this.center.y - scaledFrameSize.height / 2,
+      },
+      dimensions: scaledFrameSize,
+    };
+
+    this.unscaledFrame = ensureInBounds(requestedUnscaledFrame, scaledBounds);
+    this.scaledFrame = ensureInBounds(requestedScaledFrame, this.bounds);
+
+    this.center = {
+      x: this.scaledFrame.origin.x + this.scaledFrame.dimensions.width / 2,
+      y: this.scaledFrame.origin.y + this.scaledFrame.dimensions.height / 2,
+    };
+  }
+}
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util_test.js b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util_test.js
new file mode 100644
index 0000000..80cfa36
--- /dev/null
+++ b/polygerrit-ui/app/elements/diff/gr-diff-image-viewer/util_test.js
@@ -0,0 +1,171 @@
+/**
+ * @license
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import '../../../test/common-test-setup-karma.js';
+import {FrameConstrainer} from './util.js';
+
+suite('FrameConstrainer tests', () => {
+  let constrainer;
+
+  setup(() => {
+    constrainer = new FrameConstrainer();
+    constrainer.setBounds({width: 100, height: 100});
+    constrainer.setFrameSize({width: 50, height: 50});
+    constrainer.requestCenter({x: 50, y: 50});
+  });
+
+  suite('changing center', () => {
+    test('moves frame to requested position', () => {
+      constrainer.requestCenter({x: 30, y: 30});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 5, y: 5}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('keeps frame in bounds for top left corner', () => {
+      constrainer.requestCenter({x: 5, y: 5});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 0, y: 0}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('keeps frame in bounds for bottom right corner', () => {
+      constrainer.requestCenter({x: 95, y: 95});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 50, y: 50}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('handles out-of-bounds center left', () => {
+      constrainer.requestCenter({x: -5, y: 50});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 0, y: 25}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('handles out-of-bounds center right', () => {
+      constrainer.requestCenter({x: 105, y: 50});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 50, y: 25}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('handles out-of-bounds center top', () => {
+      constrainer.requestCenter({x: 50, y: -5});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 25, y: 0}, dimensions: {width: 50, height: 50}});
+    });
+
+    test('handles out-of-bounds center bottom', () => {
+      constrainer.requestCenter({x: 50, y: 105});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 25, y: 50}, dimensions: {width: 50, height: 50}});
+    });
+  });
+
+  suite('changing frame size', () => {
+    test('maintains center when decreased', () => {
+      constrainer.setFrameSize({width: 10, height: 10});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 45, y: 45}, dimensions: {width: 10, height: 10}});
+    });
+
+    test('maintains center when increased', () => {
+      constrainer.setFrameSize({width: 80, height: 80});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 10, y: 10}, dimensions: {width: 80, height: 80}});
+    });
+
+    test('updates center to remain in bounds when increased', () => {
+      constrainer.setFrameSize({width: 10, height: 10});
+      constrainer.requestCenter({x: 95, y: 95});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 90, y: 90}, dimensions: {width: 10, height: 10}});
+
+      constrainer.setFrameSize({width: 20, height: 20});
+      assert.deepEqual(
+          constrainer.getUnscaledFrame(),
+          {origin: {x: 80, y: 80}, dimensions: {width: 20, height: 20}});
+    });
+  });
+
+  suite('changing scale', () => {
+    suite('for unscaled frame', () => {
+      test('adjusts origin to maintain center when zooming in', () => {
+        constrainer.setScale(2);
+        assert.deepEqual(
+            constrainer.getUnscaledFrame(),
+            {origin: {x: 75, y: 75}, dimensions: {width: 50, height: 50}});
+      });
+
+      test('adjusts origin to maintain center when zooming out', () => {
+        constrainer.setFrameSize({width: 20, height: 20});
+        constrainer.setScale(0.5);
+        assert.deepEqual(
+            constrainer.getUnscaledFrame(),
+            {origin: {x: 15, y: 15}, dimensions: {width: 20, height: 20}});
+      });
+
+      test('keeps frame in bounds when zooming out', () => {
+        constrainer.setScale(5);
+        constrainer.requestCenter({x: 100, y: 100});
+        assert.deepEqual(
+            constrainer.getUnscaledFrame(),
+            {origin: {x: 450, y: 450}, dimensions: {width: 50, height: 50}});
+
+        constrainer.setScale(1);
+        assert.deepEqual(
+            constrainer.getUnscaledFrame(),
+            {origin: {x: 50, y: 50}, dimensions: {width: 50, height: 50}});
+      });
+    });
+
+    suite('for scaled frame', () => {
+      test('decreases frame size and maintains center when zooming in', () => {
+        constrainer.setScale(2);
+        assert.deepEqual(
+            constrainer.getScaledFrame(),
+            {origin: {x: 37.5, y: 37.5}, dimensions: {width: 25, height: 25}});
+      });
+
+      test('increases frame size and maintains center when zooming out', () => {
+        constrainer.setFrameSize({width: 20, height: 20});
+        constrainer.setScale(0.5);
+        assert.deepEqual(
+            constrainer.getScaledFrame(),
+            {origin: {x: 30, y: 30}, dimensions: {width: 40, height: 40}});
+      });
+
+      test('keeps frame in bounds when zooming out', () => {
+        constrainer.setScale(5);
+        constrainer.requestCenter({x: 100, y: 100});
+        assert.deepEqual(
+            constrainer.getScaledFrame(),
+            {origin: {x: 90, y: 90}, dimensions: {width: 10, height: 10}});
+
+        constrainer.setScale(1);
+        assert.deepEqual(
+            constrainer.getScaledFrame(),
+            {origin: {x: 50, y: 50}, dimensions: {width: 50, height: 50}});
+      });
+    });
+  });
+});
\ No newline at end of file
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
index cfe2cfe..60f2853 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
@@ -60,17 +60,17 @@
       this.restApiService.savePreferences({diff_view: newMode});
     }
     this.mode = newMode;
-    let annoucement;
+    let announcement;
     if (this.isUnifiedSelected(newMode)) {
-      annoucement = 'Changed diff view to unified';
+      announcement = 'Changed diff view to unified';
     } else if (this.isSideBySideSelected(newMode)) {
-      annoucement = 'Changed diff view to side by side';
+      announcement = 'Changed diff view to side by side';
     }
-    if (annoucement) {
+    if (announcement) {
       this.fire(
         'iron-announce',
         {
-          text: annoucement,
+          text: announcement,
         },
         {bubbles: true}
       );
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
index 088d9cf..2c4b8f6 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.ts
@@ -1465,9 +1465,9 @@
   ) {
     let patchNum = patchRange.patchNum;
 
-    const comparedAgainsParent = patchRange.basePatchNum === 'PARENT';
+    const comparedAgainstParent = patchRange.basePatchNum === 'PARENT';
 
-    if (isBase && !comparedAgainsParent) {
+    if (isBase && !comparedAgainstParent) {
       patchNum = patchRange.basePatchNum;
     }
 
@@ -1475,7 +1475,7 @@
       changeBaseURL(project, changeNum, patchNum) +
       `/files/${encodeURIComponent(path)}/download`;
 
-    if (isBase && comparedAgainsParent) {
+    if (isBase && comparedAgainstParent) {
       url += '?parent=1';
     }
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
index 66ac065..0ca929a 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
@@ -88,7 +88,7 @@
 // TODO: This type should be exposed to gr-diff clients in a separate type file.
 // For Gerrit these are instances of GrCommentThread, but other gr-diff users
 // have different HTML elements in use for comment threads.
-// TODO: Also document the required HTML attritbutes that thread elements must
+// TODO: Also document the required HTML attributes that thread elements must
 // have, e.g. 'diff-side', 'range', 'line-num', 'data-value'.
 export interface GrDiffThreadElement extends HTMLElement {
   rootId: string;
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.ts b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.ts
index 52465b3..5ab8449 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.ts
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.ts
@@ -35,7 +35,6 @@
         text-transform: none;
         font-family: var(--font-family);
       }
-      --trigger-hover-color: rgba(0, 0, 0, 0.6);
     }
     @media screen and (max-width: 50em) {
       .filesWeblinks {
diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts
index da29b85..1150674 100644
--- a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts
+++ b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.ts
@@ -492,7 +492,7 @@
    * with code it shouldn't AND to avoid executing regexes as much as
    * possible.
    * * These tests should document the issue clearly enough that the test can
-   * be condidently removed when the issue is solved in HLJS.
+   * be confidently removed when the issue is solved in HLJS.
    * * These tests should rewrite the line of code to have the same number of
    * characters. This method rewrites the string that gets parsed, but NOT
    * the string that gets displayed and highlighted. Thus, the positions
diff --git a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
index b36edd4..bc153ee 100644
--- a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
+++ b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.ts
@@ -277,7 +277,8 @@
     return this.restApiService
       .queryChangeFiles(this.change._number, this.patchNum, input)
       .then(res => {
-        if (!res) throw new Error('Failed to retrieve files. Reponse not set.');
+        if (!res)
+          throw new Error('Failed to retrieve files. Response not set.');
         return res.map(file => {
           return {name: file};
         });
diff --git a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.js b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.js
index be6ffc4..bbf4790 100644
--- a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.js
+++ b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.js
@@ -50,14 +50,14 @@
 
   suite('edit button CUJ', () => {
     let navStubs;
-    let openAutoCcmplete;
+    let openAutoComplete;
 
     setup(() => {
       navStubs = [
         sinon.stub(GerritNav, 'getEditUrlForDiff'),
         sinon.stub(GerritNav, 'navigateToRelativeUrl'),
       ];
-      openAutoCcmplete = element.$.openDialog.querySelector('gr-autocomplete');
+      openAutoComplete = element.$.openDialog.querySelector('gr-autocomplete');
     });
 
     test('_isValidPath', () => {
@@ -77,9 +77,9 @@
         assert.isFalse(queryStub.called);
         // Setup _focused manually - in headless mode Chrome sometimes don't
         // setup focus. flush and/or flushAsynchronousOperations don't help
-        openAutoCcmplete._focused = true;
-        openAutoCcmplete.noDebounce = true;
-        openAutoCcmplete.text = 'src/test.cpp';
+        openAutoComplete._focused = true;
+        openAutoComplete.noDebounce = true;
+        openAutoComplete.text = 'src/test.cpp';
         assert.isTrue(queryStub.called);
         assert.isFalse(element.$.openDialog.disabled);
         MockInteractions.tap(element.$.openDialog.shadowRoot
@@ -95,8 +95,8 @@
       MockInteractions.tap(element.shadowRoot.querySelector('#open'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.openDialog.disabled);
-        openAutoCcmplete.noDebounce = true;
-        openAutoCcmplete.text = 'src/test.cpp';
+        openAutoComplete.noDebounce = true;
+        openAutoComplete.text = 'src/test.cpp';
         assert.isFalse(element.$.openDialog.disabled);
         MockInteractions.tap(element.$.openDialog.shadowRoot
             .querySelector('gr-button'));
diff --git a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
index 1864598..1e08a5c 100644
--- a/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
+++ b/polygerrit-ui/app/elements/edit/gr-editor-view/gr-editor-view.ts
@@ -200,7 +200,7 @@
   }
 
   _handlePathChanged(e: CustomEvent<string>) {
-    // TODO(TS) could be cleand up, it was added for type requirements
+    // TODO(TS) could be cleaned up, it was added for type requirements
     if (this._changeNum === undefined || !this._path) {
       return Promise.reject(new Error('changeNum or path undefined'));
     }
diff --git a/polygerrit-ui/app/elements/plugins/gr-admin-api/gr-admin-api.ts b/polygerrit-ui/app/elements/plugins/gr-admin-api/gr-admin-api.ts
index 897be67..7a91c68 100644
--- a/polygerrit-ui/app/elements/plugins/gr-admin-api/gr-admin-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-admin-api/gr-admin-api.ts
@@ -16,6 +16,7 @@
  */
 import {EventType, PluginApi} from '../../../api/plugin';
 import {AdminPluginApi, MenuLink} from '../../../api/admin';
+import {appContext} from '../../../services/app-context';
 
 /**
  * GrAdminApi class.
@@ -26,15 +27,20 @@
   // TODO(TS): maybe define as enum if its a limited set
   private menuLinks: MenuLink[] = [];
 
+  private readonly reporting = appContext.reportingService;
+
   constructor(private readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'admin', 'constructor');
     this.plugin.on(EventType.ADMIN_MENU_LINKS, this);
   }
 
   addMenuLink(text: string, url: string, capability?: string) {
+    this.reporting.trackApi(this.plugin, 'admin', 'addMenuLink');
     this.menuLinks.push({text, url, capability: capability || null});
   }
 
   getMenuLinks(): MenuLink[] {
+    this.reporting.trackApi(this.plugin, 'admin', 'getMenuLinks');
     return this.menuLinks.slice(0);
   }
 }
diff --git a/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.ts b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.ts
index e0b4ee9..ab2ce6a 100644
--- a/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.ts
@@ -15,14 +15,20 @@
  * limitations under the License.
  */
 import {AttributeHelperPluginApi} from '../../../api/attribute-helper';
+import {PluginApi} from '../../../api/plugin';
+import {appContext} from '../../../services/app-context';
 
 export class GrAttributeHelper implements AttributeHelperPluginApi {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   private readonly _promises = new Map<string, Promise<any>>();
 
+  private readonly reporting = appContext.reportingService;
+
   // TODO(TS): Change any to something more like HTMLElement.
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  constructor(public element: any) {}
+  constructor(readonly plugin: PluginApi, public element: any) {
+    this.reporting.trackApi(this.plugin, 'attribute', 'constructor');
+  }
 
   _getChangedEventName(name: string): string {
     return name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase() + '-changed';
@@ -52,6 +58,7 @@
    */
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   bind(name: string, callback: (value: any) => void) {
+    this.reporting.trackApi(this.plugin, 'attribute', 'bind');
     const attributeChangedEventName = this._getChangedEventName(name);
     const changedHandler = (e: CustomEvent) =>
       this._reportValue(callback, e.detail.value);
@@ -72,6 +79,7 @@
    * to be initialized if it isn't defined.
    */
   get(name: string): Promise<unknown> {
+    this.reporting.trackApi(this.plugin, 'attribute', 'get');
     if (this._elementHasProperty(name)) {
       return Promise.resolve(this.element[name]);
     }
@@ -93,6 +101,7 @@
    */
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   set(name: string, value: any) {
+    this.reporting.trackApi(this.plugin, 'attribute', 'set');
     this.element[name] = value;
     this.element.dispatchEvent(
       new CustomEvent(this._getChangedEventName(name), {detail: {value}})
diff --git a/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper_test.js b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper_test.js
index ea7bdc3..2d83012 100644
--- a/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper_test.js
+++ b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper_test.js
@@ -17,10 +17,10 @@
 
 import '../../../test/common-test-setup-karma.js';
 import {Polymer} from '@polymer/polymer/lib/legacy/polymer-fn.js';
-import {GrAttributeHelper} from './gr-attribute-helper.js';
+import {_testOnly_initGerritPluginApi} from '../../shared/gr-js-api-interface/gr-gerrit.js';
 
 Polymer({
-  is: 'gr-attrubute-helper-some-element',
+  is: 'gr-attribute-helper-some-element',
   properties: {
     fooBar: {
       type: Object,
@@ -29,15 +29,20 @@
   },
 });
 
-const basicFixture = fixtureFromElement('gr-attrubute-helper-some-element');
+const basicFixture = fixtureFromElement('gr-attribute-helper-some-element');
+
+const pluginApi = _testOnly_initGerritPluginApi();
 
 suite('gr-attribute-helper tests', () => {
   let element;
   let instance;
 
   setup(() => {
+    let plugin;
+    pluginApi.install(p => { plugin = p; }, '0.1',
+        'http://test.com/plugins/testplugin/static/test.js');
     element = basicFixture.instantiate();
-    instance = new GrAttributeHelper(element);
+    instance = plugin.attributeHelper(element);
   });
 
   test('resolved on value change from undefined', () => {
diff --git a/polygerrit-ui/app/elements/plugins/gr-change-metadata-api/gr-change-metadata-api.ts b/polygerrit-ui/app/elements/plugins/gr-change-metadata-api/gr-change-metadata-api.ts
index a03c5dc..bbb58fc 100644
--- a/polygerrit-ui/app/elements/plugins/gr-change-metadata-api/gr-change-metadata-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-change-metadata-api/gr-change-metadata-api.ts
@@ -17,15 +17,19 @@
 import {PluginApi} from '../../../api/plugin';
 import {ChangeMetadataPluginApi} from '../../../api/change-metadata';
 import {HookApi} from '../../../api/hook';
+import {appContext} from '../../../services/app-context';
 
 export class GrChangeMetadataApi implements ChangeMetadataPluginApi {
   private hook: HookApi | null;
 
   public plugin: PluginApi;
 
+  private readonly reporting = appContext.reportingService;
+
   constructor(plugin: PluginApi) {
     this.plugin = plugin;
     this.hook = null;
+    this.reporting.trackApi(this.plugin, 'metadata', 'constructor');
   }
 
   _createHook() {
@@ -33,6 +37,7 @@
   }
 
   onLabelsChanged(callback: (value: unknown) => void) {
+    this.reporting.trackApi(this.plugin, 'metadata', 'onLabelsChanged');
     if (!this.hook) {
       this._createHook();
     }
diff --git a/polygerrit-ui/app/elements/plugins/gr-checks-api/gr-checks-api.ts b/polygerrit-ui/app/elements/plugins/gr-checks-api/gr-checks-api.ts
index 404fc71..39d3c8b 100644
--- a/polygerrit-ui/app/elements/plugins/gr-checks-api/gr-checks-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-checks-api/gr-checks-api.ts
@@ -43,13 +43,19 @@
 
   private readonly checksService = appContext.checksService;
 
-  constructor(readonly plugin: PluginApi) {}
+  private readonly reporting = appContext.reportingService;
+
+  constructor(readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'checks', 'constructor');
+  }
 
   announceUpdate() {
+    this.reporting.trackApi(this.plugin, 'checks', 'announceUpdate');
     this.checksService.reload(this.plugin.getPluginName());
   }
 
   register(provider: ChecksProvider, config?: ChecksApiConfig): void {
+    this.reporting.trackApi(this.plugin, 'checks', 'register');
     if (this.state === State.REGISTERED)
       throw new Error('Only one provider can be registered per plugin.');
     this.state = State.REGISTERED;
diff --git a/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper.ts b/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper.ts
index 4b34d56..0c2f412 100644
--- a/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper.ts
@@ -18,6 +18,8 @@
   EventHelperPluginApi,
   UnsubscribeCallback,
 } from '../../../api/event-helper';
+import {PluginApi} from '../../../api/plugin';
+import {appContext} from '../../../services/app-context';
 
 export interface ListenOptions {
   event?: string;
@@ -25,13 +27,18 @@
 }
 
 export class GrEventHelper implements EventHelperPluginApi {
-  constructor(readonly element: HTMLElement) {}
+  private readonly reporting = appContext.reportingService;
+
+  constructor(readonly plugin: PluginApi, readonly element: HTMLElement) {
+    this.reporting.trackApi(this.plugin, 'event', 'constructor');
+  }
 
   /**
    * Add a callback to arbitrary event.
    * The callback may return false to prevent event bubbling.
    */
   on(event: string, callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'event', 'on');
     return this._listen(this.element, callback, {event});
   }
 
@@ -39,6 +46,7 @@
    * Alias for @see onClick
    */
   onTap(callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'event', 'onTap');
     return this.onClick(callback);
   }
 
@@ -47,6 +55,7 @@
    * The callback may return false to prevent event bubbling.
    */
   onClick(callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'event', 'onClick');
     return this._listen(this.element, callback);
   }
 
@@ -54,6 +63,7 @@
    * Alias for @see captureClick
    */
   captureTap(callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'event', 'captureTap');
     return this.captureClick(callback);
   }
 
@@ -64,6 +74,7 @@
    * The callback may return false to cancel regular event listeners.
    */
   captureClick(callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'event', 'captureClick');
     const parent = this.element.parentElement!;
     return this._listen(parent, callback, {capture: true});
   }
diff --git a/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper_test.js b/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper_test.js
index 25c0d43..547b575 100644
--- a/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper_test.js
+++ b/polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-helper_test.js
@@ -17,8 +17,8 @@
 
 import '../../../test/common-test-setup-karma.js';
 import {addListener} from '@polymer/polymer/lib/utils/gestures.js';
-import {GrEventHelper} from './gr-event-helper.js';
 import {Polymer} from '@polymer/polymer/lib/legacy/polymer-fn.js';
+import {_testOnly_initGerritPluginApi} from '../../shared/gr-js-api-interface/gr-gerrit.js';
 
 Polymer({
   is: 'gr-event-helper-some-element',
@@ -33,13 +33,18 @@
 
 const basicFixture = fixtureFromElement('gr-event-helper-some-element');
 
+const pluginApi = _testOnly_initGerritPluginApi();
+
 suite('gr-event-helper tests', () => {
   let element;
   let instance;
 
   setup(() => {
+    let plugin;
+    pluginApi.install(p => { plugin = p; }, '0.1',
+        'http://test.com/plugins/testplugin/static/test.js');
     element = basicFixture.instantiate();
-    instance = new GrEventHelper(element);
+    instance = plugin.eventHelper(element);
   });
 
   test('onTap()', done => {
diff --git a/polygerrit-ui/app/elements/plugins/gr-popup-interface/gr-popup-interface.ts b/polygerrit-ui/app/elements/plugins/gr-popup-interface/gr-popup-interface.ts
index dcabc80..13d18b5 100644
--- a/polygerrit-ui/app/elements/plugins/gr-popup-interface/gr-popup-interface.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-popup-interface/gr-popup-interface.ts
@@ -19,6 +19,7 @@
 import {GrPluginPopup} from './gr-plugin-popup';
 import {PluginApi} from '../../../api/plugin';
 import {PopupPluginApi} from '../../../api/popup';
+import {appContext} from '../../../services/app-context';
 
 interface CustomPolymerPluginEl extends HTMLElement {
   plugin: PluginApi;
@@ -35,10 +36,14 @@
 
   private popup: GrPluginPopup | null = null;
 
+  private readonly reporting = appContext.reportingService;
+
   constructor(
     readonly plugin: PluginApi,
     private moduleName: string | null = null
-  ) {}
+  ) {
+    this.reporting.trackApi(this.plugin, 'popup', 'constructor');
+  }
 
   _getElement() {
     // TODO(TS): maybe consider removing this if no one is using
@@ -52,6 +57,7 @@
    * if it was provided with constructor.
    */
   open(): Promise<PopupPluginApi> {
+    this.reporting.trackApi(this.plugin, 'popup', 'open');
     if (!this.openingPromise) {
       this.openingPromise = this.plugin
         .hook('plugin-overlay')
@@ -76,6 +82,7 @@
    * Hides the popup.
    */
   close() {
+    this.reporting.trackApi(this.plugin, 'popup', 'close');
     if (!this.popup) {
       return;
     }
diff --git a/polygerrit-ui/app/elements/plugins/gr-repo-api/gr-repo-api.ts b/polygerrit-ui/app/elements/plugins/gr-repo-api/gr-repo-api.ts
index 0418edb..51e9112 100644
--- a/polygerrit-ui/app/elements/plugins/gr-repo-api/gr-repo-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-repo-api/gr-repo-api.ts
@@ -19,6 +19,7 @@
 import {PluginApi} from '../../../api/plugin';
 import {RepoCommandCallback, RepoPluginApi} from '../../../api/repo';
 import {HookApi} from '../../../api/hook';
+import {appContext} from '../../../services/app-context';
 
 /**
  * Parameters provided on repo-command endpoint
@@ -31,7 +32,11 @@
 export class GrRepoApi implements RepoPluginApi {
   private hook?: HookApi;
 
-  constructor(readonly plugin: PluginApi) {}
+  private readonly reporting = appContext.reportingService;
+
+  constructor(readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'repo', 'constructor');
+  }
 
   // TODO(TS): should mark as public since used in gr-change-metadata-api
   _createHook(title: string) {
@@ -43,6 +48,7 @@
   }
 
   createCommand(title: string, callback: RepoCommandCallback) {
+    this.reporting.trackApi(this.plugin, 'repo', 'createCommand');
     if (this.hook) {
       console.warn('Already set up.');
       return this;
@@ -57,6 +63,7 @@
   }
 
   onTap(callback: (event: Event) => boolean) {
+    this.reporting.trackApi(this.plugin, 'repo', 'onTap');
     if (!this.hook) {
       console.warn('Call createCommand first.');
       return this;
diff --git a/polygerrit-ui/app/elements/plugins/gr-settings-api/gr-settings-api.ts b/polygerrit-ui/app/elements/plugins/gr-settings-api/gr-settings-api.ts
index 4bdd40e..3f75c0a 100644
--- a/polygerrit-ui/app/elements/plugins/gr-settings-api/gr-settings-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-settings-api/gr-settings-api.ts
@@ -18,6 +18,7 @@
 import '../../settings/gr-settings-view/gr-settings-menu-item';
 import {PluginApi} from '../../../api/plugin';
 import {SettingsPluginApi} from '../../../api/settings';
+import {appContext} from '../../../services/app-context';
 
 export class GrSettingsApi implements SettingsPluginApi {
   private _token: string;
@@ -26,27 +27,34 @@
 
   private _moduleName?: string;
 
+  private readonly reporting = appContext.reportingService;
+
   constructor(readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'settings', 'constructor');
     // Generate default screen URL token, specific to plugin, and unique(ish).
     this._token = plugin.getPluginName() + Math.random().toString(36).substr(5);
   }
 
   title(newTitle: string) {
+    this.reporting.trackApi(this.plugin, 'settings', 'title');
     this._title = newTitle;
     return this;
   }
 
   token(newToken: string) {
+    this.reporting.trackApi(this.plugin, 'settings', 'token');
     this._token = newToken;
     return this;
   }
 
   module(newModuleName: string) {
+    this.reporting.trackApi(this.plugin, 'settings', 'module');
     this._moduleName = newModuleName;
     return this;
   }
 
   build() {
+    this.reporting.trackApi(this.plugin, 'settings', 'build');
     if (!this._moduleName) {
       throw new Error('Settings screen custom element not defined!');
     }
diff --git a/polygerrit-ui/app/elements/plugins/gr-styles-api/gr-styles-api.ts b/polygerrit-ui/app/elements/plugins/gr-styles-api/gr-styles-api.ts
index a91b8d3..9a15bf5 100644
--- a/polygerrit-ui/app/elements/plugins/gr-styles-api/gr-styles-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-styles-api/gr-styles-api.ts
@@ -15,6 +15,8 @@
  * limitations under the License.
  */
 import {StyleObject, StylesPluginApi} from '../../../api/styles';
+import {appContext} from '../../../services/app-context';
+import {PluginApi} from '../../../api/plugin';
 
 /**
  * @fileoverview We should consider dropping support for this API:
@@ -77,10 +79,17 @@
  * TODO(TS): move to util
  */
 export class GrStylesApi implements StylesPluginApi {
+  private readonly reporting = appContext.reportingService;
+
+  constructor(readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'styles', 'constructor');
+  }
+
   /**
    * Creates a new GrStyleObject with specified style properties.
    */
   css(ruleStr: string) {
+    this.reporting.trackApi(this.plugin, 'styles', 'css');
     return new GrStyleObject(ruleStr);
   }
 }
diff --git a/polygerrit-ui/app/elements/plugins/gr-theme-api/gr-theme-api.ts b/polygerrit-ui/app/elements/plugins/gr-theme-api/gr-theme-api.ts
index 894ec6c..c7be7f6 100644
--- a/polygerrit-ui/app/elements/plugins/gr-theme-api/gr-theme-api.ts
+++ b/polygerrit-ui/app/elements/plugins/gr-theme-api/gr-theme-api.ts
@@ -18,14 +18,20 @@
 import {GrCustomPluginHeader} from './gr-custom-plugin-header';
 import {PluginApi} from '../../../api/plugin';
 import {ThemePluginApi} from '../../../api/theme';
+import {appContext} from '../../../services/app-context';
 
 /**
  * Defines api for theme, can be used to set header logo and title.
  */
 export class GrThemeApi implements ThemePluginApi {
-  constructor(private readonly plugin: PluginApi) {}
+  private readonly reporting = appContext.reportingService;
+
+  constructor(private readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'theme', 'constructor');
+  }
 
   setHeaderLogoAndTitle(logoUrl: string, title: string) {
+    this.reporting.trackApi(this.plugin, 'theme', 'setHeaderLogoAndTitle');
     this.plugin.hook('header-title', {replace: true}).onAttached(element => {
       const customHeader: GrCustomPluginHeader = document.createElement(
         'gr-custom-plugin-header'
diff --git a/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_html.ts b/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_html.ts
index 91ca402..59203d3 100644
--- a/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_html.ts
+++ b/polygerrit-ui/app/elements/settings/gr-cla-view/gr-cla-view_html.ts
@@ -25,7 +25,7 @@
       margin-bottom: var(--spacing-m);
     }
     .agreementsUrl {
-      border: 1px solid #b0bdcc;
+      border: 1px solid var(--border-color);
       margin-bottom: var(--spacing-xl);
       margin-left: var(--spacing-xl);
       margin-right: var(--spacing-xl);
diff --git a/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip_html.ts b/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip_html.ts
index 3bb1458..4e6dd1a 100644
--- a/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-account-chip/gr-account-chip_html.ts
@@ -58,7 +58,6 @@
     gr-button.remove:focus {
       --gr-button: {
         @apply --gr-remove-button-style;
-        color: #333;
       }
     }
     gr-button.remove {
diff --git a/polygerrit-ui/app/elements/shared/gr-avatar/gr-avatar_html.ts b/polygerrit-ui/app/elements/shared/gr-avatar/gr-avatar_html.ts
index d105c5d..e55c8f1 100644
--- a/polygerrit-ui/app/elements/shared/gr-avatar/gr-avatar_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-avatar/gr-avatar_html.ts
@@ -22,7 +22,7 @@
       display: inline-block;
       border-radius: 50%;
       background-size: cover;
-      background-color: var(--avatar-background-color, #f1f2f3);
+      background-color: var(--avatar-background-color, var(--gray-background));
     }
   </style>
 `;
diff --git a/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts b/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
index 7a6ce2c..60b891e 100644
--- a/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
+++ b/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
@@ -61,7 +61,7 @@
   tooltip = '';
 
   // Note: don't assign a value to this, since constructor is called
-  // after created, the initial value maybe overriden by this
+  // after created, the initial value maybe overridden by this
   @property({type: String})
   _initialTabindex?: string;
 
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
index 76bbd67..55408c0 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
@@ -23,12 +23,12 @@
       font-size: var(--font-size-normal);
       font-weight: var(--font-weight-normal);
       line-height: var(--line-height-normal);
-      /* Explicitly set the background color of the diff to be white. We
+      /* Explicitly set the background color of the diff. We
        * cannot use the diff content type ab because of the skip chunk preceding
        * it, diff processor assumes the chunk of type skip/ab can be collapsed
        * and hides our diff behind context control buttons.
        *  */
-      --dark-add-highlight-color: white;
+      --dark-add-highlight-color: var(--background-color-primary);
     }
     gr-button {
       margin-left: var(--spacing-m);
diff --git a/polygerrit-ui/app/elements/shared/gr-cursor-manager/gr-cursor-manager.ts b/polygerrit-ui/app/elements/shared/gr-cursor-manager/gr-cursor-manager.ts
index 2fbbd7c..119ed20 100644
--- a/polygerrit-ui/app/elements/shared/gr-cursor-manager/gr-cursor-manager.ts
+++ b/polygerrit-ui/app/elements/shared/gr-cursor-manager/gr-cursor-manager.ts
@@ -54,8 +54,8 @@
 export type Stop = HTMLElement | AbortStop;
 
 /**
- * Type guard and checker to check if a stop can be targetted.
- * Abort stops cannot be targetted.
+ * Type guard and checker to check if a stop can be targeted.
+ * Abort stops cannot be targeted.
  */
 export function isTargetable(stop: Stop): stop is HTMLElement {
   return !(stop instanceof AbortStop);
diff --git a/polygerrit-ui/app/elements/shared/gr-download-commands/gr-download-commands.ts b/polygerrit-ui/app/elements/shared/gr-download-commands/gr-download-commands.ts
index d2f003b..4c2a417 100644
--- a/polygerrit-ui/app/elements/shared/gr-download-commands/gr-download-commands.ts
+++ b/polygerrit-ui/app/elements/shared/gr-download-commands/gr-download-commands.ts
@@ -52,7 +52,7 @@
 
   // TODO(TS): maybe default to [] as only used in dom-repeat
   @property({type: Array})
-  comamnds?: Command[];
+  commands?: Command[];
 
   @property({type: Boolean})
   _loggedIn = false;
diff --git a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
index 3fce16e..888f34f 100644
--- a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
+++ b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
@@ -32,7 +32,7 @@
 import {NormalizedFileInfo} from '../../change/gr-file-list/gr-file-list';
 
 /**
- * Requred values are text and value. mobileText and triggerText will
+ * Required values are text and value. mobileText and triggerText will
  * fall back to text if not provided.
  *
  * If bottomText is not provided, nothing will display on the second
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
index c744eab..2780fbe 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
@@ -120,6 +120,8 @@
 
   private readonly flagsService = appContext.flagsService;
 
+  private readonly reporting = appContext.reportingService;
+
   /** @override */
   ready() {
     super.ready();
@@ -238,6 +240,10 @@
 
   _toggleCommitCollapsed() {
     this._commitCollapsed = !this._commitCollapsed;
+    this.reporting.reportInteraction('toggle show all button', {
+      sectionName: 'Commit message',
+      toState: !this._commitCollapsed ? 'Show all' : 'Show less',
+    });
     if (this._commitCollapsed) {
       window.scrollTo(0, 0);
     }
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
index 374cc62..0f530bf 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
@@ -68,6 +68,11 @@
       border-radius: 0 0 4px 4px;
       border-color: var(--border-color);
       box-shadow: var(--elevation-level-1);
+      /* slightly up to cover rounded corner of the commit msg */
+      margin-top: calc(-1 * var(--spacing-xs));
+      /* To make this bar pop over editor, since editor has relative position. 
+      */
+      position: relative;
     }
     .show-all-container .show-all-button {
       margin-right: auto;
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-annotation-actions-js-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-annotation-actions-js-api.ts
index a3d038d..857d079 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-annotation-actions-js-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-annotation-actions-js-api.ts
@@ -41,10 +41,12 @@
   private readonly reporting = appContext.reportingService;
 
   constructor(private readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'annotation', 'constructor');
     plugin.on(EventType.ANNOTATE_DIFF, this);
   }
 
   setLayer(annotationCallback: AnnotationCallback) {
+    this.reporting.trackApi(this.plugin, 'annotation', 'setLayer');
     if (this.annotationCallback) {
       console.warn('Overwriting an existing plugin annotation layer.');
     }
@@ -55,6 +57,7 @@
   setCoverageProvider(
     coverageProvider: CoverageProvider
   ): GrAnnotationActionsInterface {
+    this.reporting.trackApi(this.plugin, 'annotation', 'setCoverageProvider');
     if (this.coverageProvider) {
       console.warn('Overwriting an existing coverage provider.');
     }
@@ -74,6 +77,7 @@
     checkboxLabel: string,
     onAttached: (checkboxEl: Element | null) => void
   ) {
+    this.reporting.trackApi(this.plugin, 'annotation', 'enableToggleCheckbox');
     this.plugin.hook('annotation-toggler').onAttached(element => {
       if (!element.content) {
         this.reporting.error(new Error('plugin endpoint without content.'));
@@ -104,6 +108,7 @@
   }
 
   notify(path: string, start: number, end: number, side: Side) {
+    this.reporting.trackApi(this.plugin, 'annotation', 'notify');
     for (const annotationLayer of this.annotationLayers) {
       // Notify only the annotation layer that is associated with the specified
       // path.
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api.ts
index a4c6974..15d4680 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api.ts
@@ -68,7 +68,10 @@
 
   ActionType = ActionType;
 
+  private readonly reporting = appContext.reportingService;
+
   constructor(public plugin: PluginApi, el?: GrChangeActionsElement) {
+    this.reporting.trackApi(this.plugin, 'actions', 'constructor');
     this.setEl(el);
   }
 
@@ -100,6 +103,7 @@
   }
 
   addPrimaryActionKey(key: PrimaryActionKey) {
+    this.reporting.trackApi(this.plugin, 'actions', 'addPrimaryActionKey');
     const el = this.ensureEl();
     if (el.primaryActionKeys.includes(key)) {
       return;
@@ -109,63 +113,77 @@
   }
 
   removePrimaryActionKey(key: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'removePrimaryActionKey');
     const el = this.ensureEl();
     el.primaryActionKeys = el.primaryActionKeys.filter(k => k !== key);
   }
 
   hideQuickApproveAction() {
+    this.reporting.trackApi(this.plugin, 'actions', 'hideQuickApproveAction');
     this.ensureEl().hideQuickApproveAction();
   }
 
   setActionOverflow(type: ActionType, key: string, overflow: boolean) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setActionOverflow');
     // TODO(TS): remove return, unclear why it was written
     return this.ensureEl().setActionOverflow(type, key, overflow);
   }
 
   setActionPriority(type: ActionType, key: string, priority: ActionPriority) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setActionPriority');
     // TODO(TS): remove return, unclear why it was written
     return this.ensureEl().setActionPriority(type, key, priority);
   }
 
   setActionHidden(type: ActionType, key: string, hidden: boolean) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setActionHidden');
     // TODO(TS): remove return, unclear why it was written
     return this.ensureEl().setActionHidden(type, key, hidden);
   }
 
   add(type: ActionType, label: string): string {
+    this.reporting.trackApi(this.plugin, 'actions', 'add');
     return this.ensureEl().addActionButton(type, label);
   }
 
   remove(key: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'remove');
     // TODO(TS): remove return, unclear why it was written
     return this.ensureEl().removeActionButton(key);
   }
 
   addTapListener(key: string, handler: EventListenerOrEventListenerObject) {
+    this.reporting.trackApi(this.plugin, 'actions', 'addTapListener');
     this.ensureEl().addEventListener(key + '-tap', handler);
   }
 
   removeTapListener(key: string, handler: EventListenerOrEventListenerObject) {
+    this.reporting.trackApi(this.plugin, 'actions', 'removeTapListener');
     this.ensureEl().removeEventListener(key + '-tap', handler);
   }
 
   setLabel(key: string, text: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setLabel');
     this.ensureEl().setActionButtonProp(key, 'label', text);
   }
 
   setTitle(key: string, text: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setTitle');
     this.ensureEl().setActionButtonProp(key, 'title', text);
   }
 
   setEnabled(key: string, enabled: boolean) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setEnabled');
     this.ensureEl().setActionButtonProp(key, 'enabled', enabled);
   }
 
   setIcon(key: string, icon: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'setIcon');
     this.ensureEl().setActionButtonProp(key, 'icon', icon);
   }
 
   getActionDetails(action: string) {
+    this.reporting.trackApi(this.plugin, 'actions', 'getActionDetails');
     const el = this.ensureEl();
     return (
       el.getActionDetails(action) ||
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-reply-js-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-reply-js-api.ts
index effebe1..de57794 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-reply-js-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-reply-js-api.ts
@@ -25,15 +25,20 @@
   ReplyChangedCallback,
   ValueChangedDetail,
 } from '../../../api/change-reply';
+import {appContext} from '../../../services/app-context';
 
 /**
  * GrChangeReplyInterface, provides a set of handy methods on reply dialog.
  */
 export class GrChangeReplyInterface implements ChangeReplyPluginApi {
+  private readonly reporting = appContext.reportingService;
+
   constructor(
     readonly plugin: PluginApi,
     readonly sharedApiElement: JsApiService
-  ) {}
+  ) {
+    this.reporting.trackApi(this.plugin, 'reply', 'constructor');
+  }
 
   get _el(): GrReplyDialog {
     return (this.sharedApiElement.getElement(
@@ -42,18 +47,22 @@
   }
 
   getLabelValue(label: string): string {
+    this.reporting.trackApi(this.plugin, 'reply', 'getLabelValue');
     return this._el.getLabelValue(label);
   }
 
   setLabelValue(label: string, value: string) {
+    this.reporting.trackApi(this.plugin, 'reply', 'setLabelValue');
     this._el.setLabelValue(label, value);
   }
 
   send(includeComments?: boolean) {
+    this.reporting.trackApi(this.plugin, 'reply', 'send');
     this._el.send(includeComments);
   }
 
   addReplyTextChangedCallback(handler: ReplyChangedCallback) {
+    this.reporting.trackApi(this.plugin, 'reply', 'addReplyTextChangedCb');
     const hookApi = this.plugin.hook('reply-text');
     const registeredHandler = (e: Event) => {
       const ce = e as CustomEvent<ValueChangedDetail>;
@@ -74,6 +83,7 @@
   }
 
   addLabelValuesChangedCallback(handler: LabelsChangedCallback) {
+    this.reporting.trackApi(this.plugin, 'reply', 'addLabelValuesChangedCb');
     const hookApi = this.plugin.hook('reply-label-scores');
     const registeredHandler = (e: Event) => {
       const ce = e as CustomEvent<LabelsChangedDetail>;
@@ -95,6 +105,7 @@
   }
 
   showMessage(message: string) {
+    this.reporting.trackApi(this.plugin, 'reply', 'showMessage');
     this._el.setPluginMessage(message);
   }
 }
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.ts
index 27bc591..7f9218a 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.ts
@@ -250,7 +250,7 @@
    *   });
    * });
    *
-   * // Listen on your-special-event from pluignB
+   * // Listen on your-special-event from pluginB
    * Gerrit.install(pluginB => {
    *   Gerrit.on("your-special-event", ({plugin}) => {
    *     // do something, plugin is pluginA
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.ts
index 8c0fce26..db34e5a 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.ts
@@ -74,7 +74,7 @@
 const UNKNOWN_PLUGIN_PREFIX = '__$$__';
 
 // Current API version for Plugin,
-// plugins with incompatible version will not be laoded.
+// plugins with incompatible version will not be loaded.
 const API_VERSION = '0.1';
 
 /**
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.js
index 6b62291..f5b1fca 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.js
@@ -225,7 +225,7 @@
     assert.isTrue(alertStub.calledTwice);
   });
 
-  test('plugins installed failed becasue of wrong version', async () => {
+  test('plugins installed failed because of wrong version', async () => {
     const plugins = [
       'http://test.com/plugins/foo/static/test.js',
       'http://test.com/plugins/bar/static/test.js',
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-rest-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-rest-api.ts
index cd35d4e..150c45a 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-rest-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-rest-api.ts
@@ -18,6 +18,7 @@
 import {RequestPayload} from '../../../types/common';
 import {appContext} from '../../../services/app-context';
 import {ErrorCallback, RestPluginApi} from '../../../api/rest';
+import {PluginApi} from '../../../api/plugin';
 
 async function getErrorMessage(response: Response): Promise<string> {
   const text = await response.text();
@@ -36,33 +37,44 @@
 export class GrPluginRestApi implements RestPluginApi {
   private readonly restApi = appContext.restApiService;
 
-  constructor(private readonly prefix = '') {}
+  private readonly reporting = appContext.reportingService;
+
+  constructor(readonly plugin: PluginApi, private readonly prefix = '') {
+    this.reporting.trackApi(this.plugin, 'rest', 'constructor');
+  }
 
   getLoggedIn() {
+    this.reporting.trackApi(this.plugin, 'rest', 'getLoggedIn');
     return this.restApi.getLoggedIn();
   }
 
   getVersion() {
+    this.reporting.trackApi(this.plugin, 'rest', 'getVersion');
     return this.restApi.getVersion();
   }
 
   getConfig() {
+    this.reporting.trackApi(this.plugin, 'rest', 'getConfig');
     return this.restApi.getConfig();
   }
 
   invalidateReposCache() {
+    this.reporting.trackApi(this.plugin, 'rest', 'invalidateReposCache');
     this.restApi.invalidateReposCache();
   }
 
   getAccount() {
+    this.reporting.trackApi(this.plugin, 'rest', 'getAccount');
     return this.restApi.getAccount();
   }
 
   getAccountCapabilities(capabilities: string[]) {
+    this.reporting.trackApi(this.plugin, 'rest', 'getAccountCapabilities');
     return this.restApi.getAccountCapabilities(capabilities);
   }
 
   getRepos(filter: string, reposPerPage: number, offset?: number) {
+    this.reporting.trackApi(this.plugin, 'rest', 'getRepos');
     return this.restApi.getRepos(filter, reposPerPage, offset);
   }
 
@@ -100,6 +112,7 @@
     errFn?: ErrorCallback,
     contentType?: string
   ): Promise<Response | void> {
+    this.reporting.trackApi(this.plugin, 'rest', 'fetch');
     return this.restApi.send(
       method,
       this.prefix + url,
@@ -119,6 +132,7 @@
     errFn?: ErrorCallback,
     contentType?: string
   ) {
+    this.reporting.trackApi(this.plugin, 'rest', 'send');
     // Plugins typically don't want Gerrit to show error dialogs for failed
     // requests. So we are defining a default errFn here, even if it is not
     // explicitly set by the caller.
@@ -167,6 +181,7 @@
   }
 
   get(url: string) {
+    this.reporting.trackApi(this.plugin, 'rest', 'get');
     return this.send(HttpMethod.GET, url);
   }
 
@@ -176,6 +191,7 @@
     errFn?: ErrorCallback,
     contentType?: string
   ) {
+    this.reporting.trackApi(this.plugin, 'rest', 'post');
     return this.send(HttpMethod.POST, url, payload, errFn, contentType);
   }
 
@@ -185,10 +201,12 @@
     errFn?: ErrorCallback,
     contentType?: string
   ) {
+    this.reporting.trackApi(this.plugin, 'rest', 'put');
     return this.send(HttpMethod.PUT, url, payload, errFn, contentType);
   }
 
   delete(url: string) {
+    this.reporting.trackApi(this.plugin, 'rest', 'delete');
     return this.fetch(HttpMethod.DELETE, url).then(response => {
       if (response.status !== 204) {
         return response.text().then(text => {
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.ts
index e7843af..68fb96b 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.ts
@@ -54,6 +54,7 @@
 import {ChangeReplyPluginApi} from '../../../api/change-reply';
 import {RestPluginApi} from '../../../api/rest';
 import {HookApi, RegisterOptions} from '../../../api/hook';
+import {AttributeHelperPluginApi} from '../../../api/attribute-helper';
 
 /**
  * Plugin-provided custom components can affect content in extension
@@ -84,6 +85,8 @@
 
   private readonly jsApi = appContext.jsApiService;
 
+  private readonly report = appContext.reportingService;
+
   constructor(url?: string) {
     this.domHooks = new GrDomHooksManager(this);
 
@@ -97,6 +100,7 @@
 
     this._url = new URL(url);
     this._name = getPluginNameFromUrl(this._url) ?? 'NULL';
+    this.report.trackApi(this, 'plugin', 'constructor');
   }
 
   getPluginName() {
@@ -104,6 +108,7 @@
   }
 
   registerStyleModule(endpoint: string, moduleName: string) {
+    this.report.trackApi(this, 'plugin', 'registerStyleModule');
     getPluginEndpoints().registerModule(this, {
       endpoint,
       type: EndpointType.STYLE,
@@ -119,6 +124,7 @@
     moduleName?: string,
     options?: RegisterOptions
   ): HookApi {
+    this.report.trackApi(this, 'plugin', 'registerCustomComponent');
     return this._registerCustomComponent(endpointName, moduleName, options);
   }
 
@@ -133,6 +139,7 @@
     moduleName?: string,
     options?: RegisterOptions
   ): HookApi {
+    this.report.trackApi(this, 'plugin', 'registerDynamicCustomComponent');
     const fullEndpointName = `${endpointName}-${this.getPluginName()}`;
     return this._registerCustomComponent(
       fullEndpointName,
@@ -169,19 +176,23 @@
    * element for the first call.
    */
   hook(endpointName: string, options?: RegisterOptions) {
+    this.report.trackApi(this, 'plugin', 'hook');
     return this.registerCustomComponent(endpointName, undefined, options);
   }
 
   getServerInfo() {
+    this.report.trackApi(this, 'plugin', 'getServerInfo');
     return appContext.restApiService.getConfig();
   }
 
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   on(eventName: EventType, callback: (...args: any[]) => any) {
+    this.report.trackApi(this, 'plugin', 'on');
     this.jsApi.addEventCallback(eventName, callback);
   }
 
   url(path?: string) {
+    this.report.trackApi(this, 'plugin', 'url');
     if (!this._url) throw new Error('plugin url not set');
     const relPath = '/plugins/' + this._name + (path || '/');
     const sameOriginPath = window.location.origin + `${getBaseUrl()}${relPath}`;
@@ -200,6 +211,7 @@
   }
 
   screenUrl(screenName?: string) {
+    this.report.trackApi(this, 'plugin', 'screenUrl');
     const origin = location.origin;
     const base = getBaseUrl();
     const tokenPart = screenName ? '/' + screenName : '';
@@ -216,21 +228,25 @@
   }
 
   get(url: string, callback?: SendCallback) {
+    this.report.trackApi(this, 'plugin', 'get');
     console.warn('.get() is deprecated! Use .restApi().get()');
     return this._send(HttpMethod.GET, url, callback);
   }
 
   post(url: string, payload: RequestPayload, callback?: SendCallback) {
+    this.report.trackApi(this, 'plugin', 'post');
     console.warn('.post() is deprecated! Use .restApi().post()');
     return this._send(HttpMethod.POST, url, callback, payload);
   }
 
   put(url: string, payload: RequestPayload, callback?: SendCallback) {
+    this.report.trackApi(this, 'plugin', 'put');
     console.warn('.put() is deprecated! Use .restApi().put()');
     return this._send(HttpMethod.PUT, url, callback, payload);
   }
 
   delete(url: string, callback?: SendCallback) {
+    this.report.trackApi(this, 'plugin', 'delete');
     console.warn('.delete() is deprecated! Use plugin.restApi().delete()');
     return this.restApi()
       .delete(this.url(url))
@@ -286,19 +302,19 @@
   }
 
   styles(): StylesPluginApi {
-    return new GrStylesApi();
+    return new GrStylesApi(this);
   }
 
   restApi(prefix?: string): RestPluginApi {
-    return new GrPluginRestApi(prefix);
+    return new GrPluginRestApi(this, prefix);
   }
 
-  attributeHelper(element: HTMLElement) {
-    return new GrAttributeHelper(element);
+  attributeHelper(element: HTMLElement): AttributeHelperPluginApi {
+    return new GrAttributeHelper(this, element);
   }
 
   eventHelper(element: HTMLElement): EventHelperPluginApi {
-    return new GrEventHelper(element);
+    return new GrEventHelper(this, element);
   }
 
   popup(): Promise<PopupPluginApi>;
@@ -314,6 +330,7 @@
   }
 
   screen(screenName: string, moduleName?: string) {
+    this.report.trackApi(this, 'plugin', 'screen');
     if (moduleName && typeof moduleName !== 'string') {
       console.error(
         '.screen(pattern, callback) deprecated, use ' +
@@ -328,6 +345,7 @@
   }
 
   _getScreenName(screenName: string) {
+    this.report.trackApi(this, 'plugin', '_getScreenName');
     return `${this.getPluginName()}-screen-${screenName}`;
   }
 }
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-reporting-js-api.ts b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-reporting-js-api.ts
index d4b51a8..205f0fe 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-reporting-js-api.ts
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-reporting-js-api.ts
@@ -25,9 +25,12 @@
 export class GrReportingJsApi implements ReportingPluginApi {
   private readonly reporting = appContext.reportingService;
 
-  constructor(private readonly plugin: PluginApi) {}
+  constructor(private readonly plugin: PluginApi) {
+    this.reporting.trackApi(this.plugin, 'reporting', 'constructor');
+  }
 
   reportInteraction(eventName: string, details?: EventDetails) {
+    this.reporting.trackApi(this.plugin, 'reporting', 'reportInteraction');
     this.reporting.reportInteraction(
       `${this.plugin.getPluginName()}-${eventName}`,
       details
@@ -35,6 +38,7 @@
   }
 
   reportLifeCycle(eventName: string, details?: EventDetails) {
+    this.reporting.trackApi(this.plugin, 'reporting', 'reportLifeCycle');
     this.reporting.reportLifeCycle(
       `${this.plugin.getPluginName()}-${eventName}`,
       details
diff --git a/polygerrit-ui/app/elements/shared/gr-linked-chip/gr-linked-chip_html.ts b/polygerrit-ui/app/elements/shared/gr-linked-chip/gr-linked-chip_html.ts
index a335db7..8581a0c 100644
--- a/polygerrit-ui/app/elements/shared/gr-linked-chip/gr-linked-chip_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-linked-chip/gr-linked-chip_html.ts
@@ -46,7 +46,6 @@
     gr-button.remove:focus {
       --gr-button: {
         @apply --gr-remove-button-style;
-        color: #333;
       }
     }
     gr-button.remove {
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
index 68f15dc..89abd57 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
@@ -457,7 +457,7 @@
    * Send an XHR.
    *
    * @return Promise resolves to Response/ParsedJSON only if the request is successful
-   *     (i.e. no exception and response.ok is trsue). If response fails then
+   *     (i.e. no exception and response.ok is true). If response fails then
    *     promise resolves either to void if errFn is set or rejects if errFn
    *     is not set   */
   send(req: SendRequest): Promise<Response | ParsedJSON | undefined> {
diff --git a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
index b0b40dd..885db2a 100644
--- a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
+++ b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.ts
@@ -112,7 +112,7 @@
   @property({type: Boolean})
   hideBorder = false;
 
-  /** Text input should be rendered in monspace font.  */
+  /** Text input should be rendered in monospace font.  */
   @property({type: Boolean})
   monospace = false;
 
diff --git a/polygerrit-ui/app/mixins/gr-tooltip-mixin/gr-tooltip-mixin.ts b/polygerrit-ui/app/mixins/gr-tooltip-mixin/gr-tooltip-mixin.ts
index 77d2d00..75ad608 100644
--- a/polygerrit-ui/app/mixins/gr-tooltip-mixin/gr-tooltip-mixin.ts
+++ b/polygerrit-ui/app/mixins/gr-tooltip-mixin/gr-tooltip-mixin.ts
@@ -69,13 +69,13 @@
       // Handler for mouseenter event
       private mouseenterHandler?: (e: MouseEvent) => void;
 
-      // Hanlder for scrolling on window
+      // Handler for scrolling on window
       private readonly windowScrollHandler: () => void;
 
-      // Hanlder for showing the tooltip, will be attached to certain events
+      // Handler for showing the tooltip, will be attached to certain events
       private readonly showHandler: () => void;
 
-      // Hanlder for hiding the tooltip, will be attached to certain events
+      // Handler for hiding the tooltip, will be attached to certain events
       private readonly hideHandler: () => void;
 
       // eslint-disable-next-line @typescript-eslint/no-unused-vars, @typescript-eslint/no-explicit-any
diff --git a/polygerrit-ui/app/mixins/iron-fit-mixin/iron-fit-mixin.ts b/polygerrit-ui/app/mixins/iron-fit-mixin/iron-fit-mixin.ts
index 662d6bf..57e034f 100644
--- a/polygerrit-ui/app/mixins/iron-fit-mixin/iron-fit-mixin.ts
+++ b/polygerrit-ui/app/mixins/iron-fit-mixin/iron-fit-mixin.ts
@@ -29,7 +29,7 @@
 // is used. To ensure that this import can't be avoided, the second parameter
 // is added. Usage example:
 // class Element extends IronFitMixin(PolymerElement, IronFitBehavior as IronFitBehavior)
-// The code 'IronFitBehavior as IronFitBehavior' required, becuase IronFitBehavior
+// The code 'IronFitBehavior as IronFitBehavior' required, because IronFitBehavior
 // defined as an object, not as IronFitBehavior instance.
 
 export const IronFitMixin = <T extends Constructor<PolymerElement>>(
diff --git a/polygerrit-ui/app/mixins/keyboard-shortcut-mixin/keyboard-shortcut-mixin.ts b/polygerrit-ui/app/mixins/keyboard-shortcut-mixin/keyboard-shortcut-mixin.ts
index 63a05aa..ab85b87 100644
--- a/polygerrit-ui/app/mixins/keyboard-shortcut-mixin/keyboard-shortcut-mixin.ts
+++ b/polygerrit-ui/app/mixins/keyboard-shortcut-mixin/keyboard-shortcut-mixin.ts
@@ -544,7 +544,7 @@
 }
 
 /**
- * Shortcut manager, holds all hosts, bindings and listners.
+ * Shortcut manager, holds all hosts, bindings and listeners.
  */
 export class ShortcutManager {
   private readonly activeHosts = new Map<PolymerElement, Map<string, string>>();
diff --git a/polygerrit-ui/app/node_modules_licenses/licenses.ts b/polygerrit-ui/app/node_modules_licenses/licenses.ts
index 7a6253b..f03c7e6 100644
--- a/polygerrit-ui/app/node_modules_licenses/licenses.ts
+++ b/polygerrit-ui/app/node_modules_licenses/licenses.ts
@@ -254,6 +254,14 @@
     license: SharedLicenses.Polymer2017
   },
   {
+    name: "@types/resize-observer-browser",
+    license: {
+      name: 'DefinitelyTyped',
+      type: LicenseTypes.Mit,
+      packageLicenseFile: "LICENSE"
+    }
+  },
+  {
     name: "@webcomponents/shadycss",
     license: SharedLicenses.Polymer2017
   },
diff --git a/polygerrit-ui/app/package.json b/polygerrit-ui/app/package.json
index 3351386..5e15990 100644
--- a/polygerrit-ui/app/package.json
+++ b/polygerrit-ui/app/package.json
@@ -25,6 +25,7 @@
     "@polymer/paper-tabs": "^3.1.0",
     "@polymer/paper-toggle-button": "^3.0.1",
     "@polymer/polymer": "^3.4.1",
+    "@types/resize-observer-browser": "^0.1.5",
     "@webcomponents/shadycss": "^1.9.2",
     "@webcomponents/webcomponentsjs": "^1.3.3",
     "ba-linkify": "file:../../lib/ba-linkify/src/",
diff --git a/polygerrit-ui/app/services/app-context-init.ts b/polygerrit-ui/app/services/app-context-init.ts
index 09e0724..0369ccf 100644
--- a/polygerrit-ui/app/services/app-context-init.ts
+++ b/polygerrit-ui/app/services/app-context-init.ts
@@ -70,7 +70,7 @@
     eventEmitter: () => new EventEmitter(),
     authService: () => new Auth(appContext.eventEmitter),
     restApiService: () => new GrRestApiInterface(appContext.authService),
-    changeService: () => new ChangeService(appContext.restApiService),
+    changeService: () => new ChangeService(),
     checksService: () => new ChecksService(),
     jsApiService: () => new GrJsApiInterface(),
   });
diff --git a/polygerrit-ui/app/services/change/change-model.ts b/polygerrit-ui/app/services/change/change-model.ts
index b2bdcfe..e7472de 100644
--- a/polygerrit-ui/app/services/change/change-model.ts
+++ b/polygerrit-ui/app/services/change/change-model.ts
@@ -46,10 +46,18 @@
 // Must only be used by the change service or whatever is in control of this
 // model.
 export function updateState(change?: ParsedChangeInfo) {
-  privateState$.next({
-    ...privateState$.getValue(),
-    change,
-  });
+  const current = privateState$.getValue();
+  // We want to make it easy for subscribers to react to change changes, so we
+  // are explicitly emitting and additional `undefined` when the change number
+  // changes. So if you are subscribed to the latestPatchsetNumber for example,
+  // then you can rely on emissions even if the old and the new change have the
+  // same latestPatchsetNumber.
+  if (change !== undefined && current.change !== undefined) {
+    if (change._number !== current.change._number) {
+      privateState$.next({...current, change: undefined});
+    }
+  }
+  privateState$.next({...current, change});
 }
 
 /**
@@ -91,9 +99,6 @@
  *
  * Note that this selector can emit a patchNum without the change being
  * available!
- *
- * TODO: It would be good to assert/enforce somehow that currentPatchNum$ cannot
- * emit 'PARENT'.
  */
 export const currentPatchNum$: Observable<
   PatchSetNum | undefined
diff --git a/polygerrit-ui/app/services/change/change-service.ts b/polygerrit-ui/app/services/change/change-service.ts
index 6a9a5e9..c292fb5 100644
--- a/polygerrit-ui/app/services/change/change-service.ts
+++ b/polygerrit-ui/app/services/change/change-service.ts
@@ -14,28 +14,28 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 import {routerChangeNum$} from '../router/router-model';
 import {updateState} from './change-model';
-import {RestApiService} from '../gr-rest-api/gr-rest-api';
-import {switchMap, tap} from 'rxjs/operators';
-import {of, from} from 'rxjs';
+import {ParsedChangeInfo} from '../../types/types';
 
 export class ChangeService {
-  private routerChangeNumEffect = routerChangeNum$.pipe(
-    switchMap(changeNum => {
-      if (!changeNum) return of(undefined);
-      return from(this.restApiService.getChangeDetail(changeNum));
-    }),
-    tap(change => {
-      updateState(change ?? undefined);
-    })
-  );
-
-  constructor(private readonly restApiService: RestApiService) {
-    this.routerChangeNumEffect.subscribe();
+  constructor() {
+    // TODO: In the future we will want to make restApiService.getChangeDetail()
+    // calls from a switchMap() here. For now just make sure to invalidate the
+    // change when no changeNum is set.
+    routerChangeNum$.subscribe(changeNum => {
+      if (!changeNum) updateState(undefined);
+    });
   }
 
-  // TODO: Remove.
-  dontDoAnything() {}
+  /**
+   * This is a temporary indirection between change-view, which currently
+   * manages what the current change is, and the change-model, which will
+   * become the source of truth in the future. We will extract a substantial
+   * amount of code from change-view and move it into this change-service. This
+   * will take some time ...
+   */
+  updateChange(change: ParsedChangeInfo) {
+    updateState(change);
+  }
 }
diff --git a/polygerrit-ui/app/services/checks/checks-model.ts b/polygerrit-ui/app/services/checks/checks-model.ts
index 6705a85..1c5b862 100644
--- a/polygerrit-ui/app/services/checks/checks-model.ts
+++ b/polygerrit-ui/app/services/checks/checks-model.ts
@@ -26,6 +26,7 @@
   RunStatus,
 } from '../../api/checks';
 import {distinctUntilChanged, map} from 'rxjs/operators';
+import {PatchSetNumber} from '../../types/common';
 
 // This is a convenience type for working with results, because when working
 // with a bunch of results you will typically also want to know about the run
@@ -34,28 +35,51 @@
 
 interface ChecksProviderState {
   pluginName: string;
+  loading: boolean;
   config?: ChecksApiConfig;
   runs: CheckRun[];
   actions: Action[];
 }
 
 interface ChecksState {
-  [name: string]: ChecksProviderState;
+  patchsetNumber?: PatchSetNumber;
+  providerNameToState: {
+    [name: string]: ChecksProviderState;
+  };
 }
 
-const initialState: ChecksState = {};
+const initialState: ChecksState = {
+  providerNameToState: {},
+};
 
 const privateState$ = new BehaviorSubject(initialState);
 
 // Re-exporting as Observable so that you can only subscribe, but not emit.
 export const checksState$: Observable<ChecksState> = privateState$;
 
-export const aPluginHasRegistered = checksState$.pipe(
+export const checksPatchsetNumber$ = checksState$.pipe(
+  map(state => state.patchsetNumber),
+  distinctUntilChanged()
+);
+
+export const checksProviderState$ = checksState$.pipe(
+  map(state => state.providerNameToState),
+  distinctUntilChanged()
+);
+
+export const aPluginHasRegistered$ = checksProviderState$.pipe(
   map(state => Object.keys(state).length > 0),
   distinctUntilChanged()
 );
 
-export const allActions$ = checksState$.pipe(
+export const someProvidersAreLoading$ = checksProviderState$.pipe(
+  map(state => {
+    return Object.values(state).some(providerState => providerState.loading);
+  }),
+  distinctUntilChanged()
+);
+
+export const allActions$ = checksProviderState$.pipe(
   map(state => {
     return Object.values(state).reduce(
       (allActions: Action[], providerState: ChecksProviderState) => [
@@ -67,7 +91,7 @@
   })
 );
 
-export const allRuns$ = checksState$.pipe(
+export const allRuns$ = checksProviderState$.pipe(
   map(state => {
     return Object.values(state).reduce(
       (allRuns: CheckRun[], providerState: ChecksProviderState) => [
@@ -79,7 +103,19 @@
   })
 );
 
-export const allResults$ = checksState$.pipe(
+export const checkToPluginMap$ = checksProviderState$.pipe(
+  map(state => {
+    const map = new Map<string, string>();
+    for (const [pluginName, providerState] of Object.entries(state)) {
+      for (const run of providerState.runs) {
+        map.set(run.checkName, pluginName);
+      }
+    }
+    return map;
+  })
+);
+
+export const allResults$ = checksProviderState$.pipe(
   map(state => {
     return Object.values(state)
       .reduce(
@@ -104,8 +140,10 @@
   config?: ChecksApiConfig
 ) {
   const nextState = {...privateState$.getValue()};
-  nextState[pluginName] = {
+  nextState.providerNameToState = {...nextState.providerNameToState};
+  nextState.providerNameToState[pluginName] = {
     pluginName,
+    loading: false,
     config,
     runs: [],
     actions: [],
@@ -177,16 +215,34 @@
   status: RunStatus.COMPLETED,
 };
 
+export function updateStateSetLoading(pluginName: string) {
+  const nextState = {...privateState$.getValue()};
+  nextState.providerNameToState = {...nextState.providerNameToState};
+  nextState.providerNameToState[pluginName] = {
+    ...nextState.providerNameToState[pluginName],
+    loading: true,
+  };
+  privateState$.next(nextState);
+}
+
 export function updateStateSetResults(
   pluginName: string,
   runs: CheckRun[],
   actions: Action[] = []
 ) {
   const nextState = {...privateState$.getValue()};
-  nextState[pluginName] = {
-    ...nextState[pluginName],
+  nextState.providerNameToState = {...nextState.providerNameToState};
+  nextState.providerNameToState[pluginName] = {
+    ...nextState.providerNameToState[pluginName],
+    loading: false,
     runs: [...runs],
     actions: [...actions],
   };
   privateState$.next(nextState);
 }
+
+export function updateStateSetPatchset(patchsetNumber?: PatchSetNumber) {
+  const nextState = {...privateState$.getValue()};
+  nextState.patchsetNumber = patchsetNumber;
+  privateState$.next(nextState);
+}
diff --git a/polygerrit-ui/app/services/checks/checks-service.ts b/polygerrit-ui/app/services/checks/checks-service.ts
index 2e63f98..fd1f810 100644
--- a/polygerrit-ui/app/services/checks/checks-service.ts
+++ b/polygerrit-ui/app/services/checks/checks-service.ts
@@ -16,9 +16,9 @@
  */
 
 import {
+  filter,
   switchMap,
   takeWhile,
-  tap,
   throttleTime,
   withLatestFrom,
 } from 'rxjs/operators';
@@ -29,8 +29,15 @@
   FetchResponse,
   ResponseCode,
 } from '../../api/checks';
-import {change$, currentPatchNum$} from '../change/change-model';
-import {updateStateSetProvider, updateStateSetResults} from './checks-model';
+import {change$, changeNum$, latestPatchNum$} from '../change/change-model';
+import {
+  updateStateSetLoading,
+  checkToPluginMap$,
+  updateStateSetProvider,
+  updateStateSetResults,
+  checksPatchsetNumber$,
+  updateStateSetPatchset,
+} from './checks-model';
 import {
   BehaviorSubject,
   combineLatest,
@@ -38,14 +45,34 @@
   Observable,
   of,
   Subject,
+  timer,
 } from 'rxjs';
+import {PatchSetNumber} from '../../types/common';
 
 export class ChecksService {
   private readonly providers: {[name: string]: ChecksProvider} = {};
 
   private readonly reloadSubjects: {[name: string]: Subject<void>} = {};
 
-  private changeAndPatchNum$ = change$.pipe(withLatestFrom(currentPatchNum$));
+  private checkToPluginMap = new Map<string, string>();
+
+  private readonly documentVisibilityChange$ = new BehaviorSubject(undefined);
+
+  constructor() {
+    checkToPluginMap$.subscribe(map => {
+      this.checkToPluginMap = map;
+    });
+    latestPatchNum$.subscribe(num => {
+      updateStateSetPatchset(num);
+    });
+    document.addEventListener('visibilitychange', () => {
+      this.documentVisibilityChange$.next(undefined);
+    });
+  }
+
+  setPatchset(num: PatchSetNumber) {
+    updateStateSetPatchset(num);
+  }
 
   reload(pluginName: string) {
     this.reloadSubjects[pluginName].next();
@@ -55,6 +82,12 @@
     Object.keys(this.providers).forEach(key => this.reload(key));
   }
 
+  reloadForCheck(checkName?: string) {
+    if (!checkName) return;
+    const plugin = this.checkToPluginMap.get(checkName);
+    if (plugin) this.reload(plugin);
+  }
+
   register(
     pluginName: string,
     provider: ChecksProvider,
@@ -63,38 +96,52 @@
     this.providers[pluginName] = provider;
     this.reloadSubjects[pluginName] = new BehaviorSubject<void>(undefined);
     updateStateSetProvider(pluginName, config);
-    // Both, changed numbers and and announceUpdate request should trigger.
+    const pollIntervalMs = (config?.fetchPollingIntervalSeconds ?? 60) * 1000;
+    // Various events should trigger fetching checks from the provider:
+    // 1. Change number and patchset number changes.
+    // 2. Specific reload requests.
+    // 3. Regular polling starting with an initial fetch right now.
+    // 4. A hidden Gerrit tab becoming visible.
     combineLatest([
-      this.changeAndPatchNum$,
+      changeNum$,
+      checksPatchsetNumber$,
       this.reloadSubjects[pluginName].pipe(throttleTime(1000)),
+      timer(0, pollIntervalMs),
+      this.documentVisibilityChange$,
     ])
       .pipe(
         takeWhile(_ => !!this.providers[pluginName]),
+        filter(_ => document.visibilityState !== 'hidden'),
+        withLatestFrom(change$),
         switchMap(
-          ([[change, patchNum], _]): Observable<FetchResponse> => {
-            if (!change || !patchNum || typeof patchNum !== 'number') {
+          ([[changeNum, patchNum], change]): Observable<FetchResponse> => {
+            if (
+              !change ||
+              !changeNum ||
+              !patchNum ||
+              typeof patchNum !== 'number'
+            ) {
               return of({
                 responseCode: ResponseCode.OK,
                 runs: [],
               });
             }
             const data: ChangeData = {
-              changeNumber: change._number,
+              changeNumber: changeNum,
               patchsetNumber: patchNum,
               repo: change.project,
             };
+            updateStateSetLoading(pluginName);
             return from(this.providers[pluginName].fetch(data));
           }
-        ),
-        tap(response => {
-          updateStateSetResults(
-            pluginName,
-            response.runs ?? [],
-            response.actions
-          );
-        })
+        )
       )
-      .subscribe(() => {});
-    this.reload(pluginName);
+      .subscribe(response => {
+        updateStateSetResults(
+          pluginName,
+          response.runs ?? [],
+          response.actions
+        );
+      });
   }
 }
diff --git a/polygerrit-ui/app/services/checks/checks-util.ts b/polygerrit-ui/app/services/checks/checks-util.ts
index 176464f..ea532ea 100644
--- a/polygerrit-ui/app/services/checks/checks-util.ts
+++ b/polygerrit-ui/app/services/checks/checks-util.ts
@@ -24,7 +24,7 @@
   return undefined;
 }
 
-export function iconForCategory(category: Category) {
+export function iconForCategory(category: Category | 'SUCCESS') {
   switch (category) {
     case Category.ERROR:
       return 'error';
@@ -32,6 +32,8 @@
       return 'info-outline';
     case Category.WARNING:
       return 'warning';
+    case 'SUCCESS':
+      return 'check-circle-outline';
     default:
       assertNever(category, `Unsupported category: ${category}`);
   }
@@ -74,8 +76,12 @@
 }
 
 export function iconForRun(run: CheckRun) {
-  const category = worstCategory(run);
-  return category ? iconForCategory(category) : iconForStatus(run.status);
+  if (run.status !== RunStatus.COMPLETED) {
+    return iconForStatus(run.status);
+  } else {
+    const category = worstCategory(run);
+    return category ? iconForCategory(category) : iconForStatus(run.status);
+  }
 }
 
 export function iconForStatus(status: RunStatus) {
diff --git a/polygerrit-ui/app/services/gr-reporting/gr-reporting.ts b/polygerrit-ui/app/services/gr-reporting/gr-reporting.ts
index 4ca983a..1be1d63 100644
--- a/polygerrit-ui/app/services/gr-reporting/gr-reporting.ts
+++ b/polygerrit-ui/app/services/gr-reporting/gr-reporting.ts
@@ -17,6 +17,7 @@
 
 import {NumericChangeId} from '../../types/common';
 import {EventDetails} from '../../api/reporting';
+import {PluginApi} from '../../api/plugin';
 
 export type EventValue = string | number | {error?: Error};
 
@@ -61,7 +62,7 @@
   timeEnd(name: string, eventDetails?: EventDetails): void;
   /**
    * Reports just line timeEnd, but additionally reports an average given a
-   * denominator and a separate reporiting name for the average.
+   * denominator and a separate reporting name for the average.
    *
    * @param name Timing name.
    * @param averageName Average timing name.
@@ -74,7 +75,7 @@
     denominator: number
   ): void;
   /**
-   * Get a timer object to for reporing a user timing. The start time will be
+   * Get a timer object for reporting a user timing. The start time will be
    * the time that the object has been created, and the end time will be the
    * time that the "end" method is called on the object.
    */
@@ -97,9 +98,10 @@
    * Every execution is only reported once per session.
    */
   reportExecution(id: string, details: EventDetails): void;
+  trackApi(plugin: PluginApi, object: string, method: string): void;
   reportInteraction(eventName: string, details?: EventDetails): void;
   /**
-   * A draft interaction was started. Update the time-betweeen-draft-actions
+   * A draft interaction was started. Update the time-between-draft-actions
    * timer.
    */
   recordDraftInteraction(): void;
diff --git a/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts b/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
index af06450..e57670d 100644
--- a/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
+++ b/polygerrit-ui/app/services/gr-reporting/gr-reporting_impl.ts
@@ -20,6 +20,7 @@
 import {hasOwnProperty} from '../../utils/common-util';
 import {NumericChangeId} from '../../types/common';
 import {EventDetails} from '../../api/reporting';
+import {PluginApi} from '../../api/plugin';
 
 // Latency reporting constants.
 
@@ -651,7 +652,7 @@
     if (baseTime !== 0) {
       window.performance.measure(name, `${name}-start`);
     } else {
-      // Microsft Edge does not handle the 2nd param correctly
+      // Microsoft Edge does not handle the 2nd param correctly
       // (if undefined).
       window.performance.measure(name);
     }
@@ -659,7 +660,7 @@
 
   /**
    * Reports just line timeEnd, but additionally reports an average given a
-   * denominator and a separate reporiting name for the average.
+   * denominator and a separate reporting name for the average.
    *
    * @param name Timing name.
    * @param averageName Average timing name.
@@ -703,7 +704,7 @@
   }
 
   /**
-   * Get a timer object to for reporing a user timing. The start time will be
+   * Get a timer object to for reporting a user timing. The start time will be
    * the time that the object has been created, and the end time will be the
    * time that the "end" method is called on the object.
    */
@@ -800,12 +801,20 @@
       id,
       undefined,
       details,
-      false
+      true // skip console log
     );
   }
 
+  trackApi(plugin: PluginApi, object: string, method: string) {
+    this.reportExecution('plugin-api', {
+      plugin: plugin.getPluginName(),
+      object,
+      method,
+    });
+  }
+
   /**
-   * A draft interaction was started. Update the time-betweeen-draft-actions
+   * A draft interaction was started. Update the time-between-draft-actions
    * timer.
    */
   recordDraftInteraction() {
diff --git a/polygerrit-ui/app/services/gr-reporting/gr-reporting_mock.ts b/polygerrit-ui/app/services/gr-reporting/gr-reporting_mock.ts
index 484ce45..7d66484 100644
--- a/polygerrit-ui/app/services/gr-reporting/gr-reporting_mock.ts
+++ b/polygerrit-ui/app/services/gr-reporting/gr-reporting_mock.ts
@@ -16,6 +16,7 @@
  */
 import {ReportingService, Timer} from './gr-reporting';
 import {EventDetails} from '../../api/reporting';
+import {PluginApi} from '../../api/plugin';
 
 export class MockTimer implements Timer {
   end(): this {
@@ -67,6 +68,9 @@
   reportExecution: (id: string, details: EventDetails) => {
     log(`reportExecution '${id}': ${JSON.stringify(details)}`);
   },
+  trackApi: (plugin: PluginApi, object: string, method: string) => {
+    log(`trackApi '${plugin}', ${object}, ${method}`);
+  },
   reportExtension: () => {},
   reportInteraction: (eventName: string, details?: EventDetails) => {
     log(`reportInteraction '${eventName}': ${JSON.stringify(details)}`);
diff --git a/polygerrit-ui/app/styles/gr-voting-styles.ts b/polygerrit-ui/app/styles/gr-voting-styles.ts
index d4e6d52..c1989de 100644
--- a/polygerrit-ui/app/styles/gr-voting-styles.ts
+++ b/polygerrit-ui/app/styles/gr-voting-styles.ts
@@ -27,7 +27,7 @@
     <style>
       :host {
         --vote-chip-styles: {
-          border: 1px solid rgba(0,0,0,.12);
+          border: 1px solid var(--border-color);
           border-radius: 1em;
           box-shadow: none;
           box-sizing: border-box;
diff --git a/polygerrit-ui/app/styles/themes/app-theme.ts b/polygerrit-ui/app/styles/themes/app-theme.ts
index c3b0681..18c12b0 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.ts
+++ b/polygerrit-ui/app/styles/themes/app-theme.ts
@@ -76,8 +76,6 @@
     --info-background: var(--blue-50);
     --selected-foreground: var(--blue-700);
     --selected-background: var(--blue-50);
-    --info-deemphasized-foreground: var(--gray-300);
-    --info-deemphasized-background: var(--gray-50);
     --success-foreground: var(--green-700);
     --success-background: var(--green-50);
     --gray-foreground: var(--gray-700);
@@ -101,6 +99,7 @@
     --tooltip-text-color: white;
     --negative-red-text-color: #d93025;
     --positive-green-text-color: #188038;
+    --indirect-ancestor-text-color: var(--green-700);
 
     /* background colors */
     /* primary background colors */
@@ -171,7 +170,7 @@
     --line-height-mono: 1.286rem;   /* 18px */
     --line-height-small: 1.143rem;  /* 16px */
     --line-height-normal: 1.429rem; /* 20px */
-    --line-height-h3: 1.714rem;     /* 24px */
+    --line-height-h3: 1.715rem;     /* 24px */
     --line-height-h2: 2rem;         /* 28px */
     --line-height-h1: 2.286rem;     /* 32px */
     --font-weight-normal: 400; /* 400 is the same as 'normal' */
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.ts b/polygerrit-ui/app/styles/themes/dark-theme.ts
index 4057f7f..5455a24 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.ts
+++ b/polygerrit-ui/app/styles/themes/dark-theme.ts
@@ -44,9 +44,10 @@
       --warning-background: var(--orange-900);
       --info-foreground: var(--blue-200);
       --info-background: var(--blue-900);
-      --info-deemphasized-foreground: var(--gray-700);
-      --info-deemphasized-background: var(--primary-text-color);
+      --selected-foreground: var(--blue-200);
+      --selected-background: var(--blue-900);
       --success-foreground: var(--green-200);
+      --success-background: var(--green-900);
       --gray-foreground: var(--gray-100);
       --gray-background: var(--gray-900);
       --tag-background: var(--cyan-900);
diff --git a/polygerrit-ui/app/tsconfig.json b/polygerrit-ui/app/tsconfig.json
index 0d751ab..46d0173d 100644
--- a/polygerrit-ui/app/tsconfig.json
+++ b/polygerrit-ui/app/tsconfig.json
@@ -48,7 +48,7 @@
   "include": [
     // Items below must be in sync with the src_dirs list in the BUILD file
     // Also items must be in sync with tsconfig_bazel.json, tsconfig_bazel_test.json
-    // (include and exclude arrays are overriden when extends)
+    // (include and exclude arrays are overridden when extends)
     "api/**/*",
     "constants/**/*",
     "elements/**/*",
diff --git a/polygerrit-ui/app/tsconfig_bazel.json b/polygerrit-ui/app/tsconfig_bazel.json
index 46bd926..dfd2078 100644
--- a/polygerrit-ui/app/tsconfig_bazel.json
+++ b/polygerrit-ui/app/tsconfig_bazel.json
@@ -9,7 +9,7 @@
   "include": [
     // Items below must be in sync with the src_dirs list in the BUILD file
     // Also items must be in sync with tsconfig.json, tsconfig_bazel_test.json
-    // (include and exclude arrays are overriden when extends)
+    // (include and exclude arrays are overridden when extends)
     "api/**/*",
     "constants/**/*",
     "elements/**/*",
diff --git a/polygerrit-ui/app/tsconfig_bazel_test.json b/polygerrit-ui/app/tsconfig_bazel_test.json
index 1b6c226..9c2ff93 100644
--- a/polygerrit-ui/app/tsconfig_bazel_test.json
+++ b/polygerrit-ui/app/tsconfig_bazel_test.json
@@ -14,7 +14,7 @@
   "include": [
     // Items below must be in sync with the src_dirs list in the BUILD file
     // Also items must be in sync with tsconfig.json, tsconfig_test.json
-    // (include and exclude arrays are overriden when extends)
+    // (include and exclude arrays are overridden when extends)
     "api/**/*",
     "constants/**/*",
     "elements/**/*",
diff --git a/polygerrit-ui/app/types/common.ts b/polygerrit-ui/app/types/common.ts
index 95801e7..1bfabf8 100644
--- a/polygerrit-ui/app/types/common.ts
+++ b/polygerrit-ui/app/types/common.ts
@@ -76,6 +76,7 @@
 export type ParsedJSON = BrandType<unknown, '_parsedJSON'>;
 
 export type PatchSetNum = BrandType<'PARENT' | 'edit' | number, '_patchSet'>;
+export type PatchSetNumber = BrandType<number, '_patchSet'>;
 
 export const EditPatchSetNum = 'edit' as PatchSetNum;
 // TODO(TS): This is not correct, it is better to have a separate ApiPatchSetNum
@@ -1021,7 +1022,7 @@
  */
 export interface PluginConfigInfo {
   has_avatars: boolean;
-  // The following 2 properies exists in Java class, but don't mention in docs
+  // The following 2 properties exists in Java class, but don't mention in docs
   js_resource_paths: string[];
   html_resource_paths: string[];
 }
diff --git a/polygerrit-ui/app/types/events.ts b/polygerrit-ui/app/types/events.ts
index 6b05fad..5965453 100644
--- a/polygerrit-ui/app/types/events.ts
+++ b/polygerrit-ui/app/types/events.ts
@@ -19,6 +19,7 @@
 import {UIComment} from '../utils/comment-util';
 import {FetchRequest} from './types';
 import {MovedLinkClickedEventDetail} from '../api/diff';
+import {Category, RunStatus} from '../api/checks';
 
 export interface TitleChangeEventDetail {
   title: string;
@@ -152,6 +153,7 @@
 
 export interface TabState {
   commentTab?: CommentTabState;
+  checksTab?: ChecksTabState;
 }
 
 export enum CommentTabState {
@@ -160,6 +162,11 @@
   SHOW_ALL = 'show all',
 }
 
+export interface ChecksTabState {
+  statusOrCategory?: RunStatus | Category;
+  checkName?: string;
+}
+
 export type SwitchTabEvent = CustomEvent<SwitchTabEventDetail>;
 
 declare global {
diff --git a/polygerrit-ui/app/utils/change-util.ts b/polygerrit-ui/app/utils/change-util.ts
index 1228863..a7f8b49 100644
--- a/polygerrit-ui/app/utils/change-util.ts
+++ b/polygerrit-ui/app/utils/change-util.ts
@@ -173,28 +173,44 @@
   return states;
 }
 
-export function isOwner(change?: ChangeInfo, account?: AccountInfo) {
+export function isOwner(change?: ChangeInfo, account?: AccountInfo): boolean {
   if (!change || !account) return false;
   return change.owner?._account_id === account._account_id;
 }
 
-export function isReviewer(change?: ChangeInfo, account?: AccountInfo) {
+export function isReviewer(
+  change?: ChangeInfo,
+  account?: AccountInfo
+): boolean {
   if (!change || !account) return false;
   const reviewers = change.reviewers.REVIEWER ?? [];
   return reviewers.some(r => r._account_id === account._account_id);
 }
 
-export function isUploader(change?: ChangeInfo, account?: AccountInfo) {
+export function isCc(change?: ChangeInfo, account?: AccountInfo): boolean {
+  if (!change || !account) return false;
+  const ccs = change.reviewers.CC ?? [];
+  return ccs.some(r => r._account_id === account._account_id);
+}
+
+export function isUploader(
+  change?: ChangeInfo,
+  account?: AccountInfo
+): boolean {
   if (!change || !account) return false;
   const rev = getCurrentRevision(change);
   return rev?.uploader?._account_id === account._account_id;
 }
 
-export function isInvolved(change?: ChangeInfo, account?: AccountInfo) {
+export function isInvolved(
+  change?: ChangeInfo,
+  account?: AccountInfo
+): boolean {
   const owner = isOwner(change, account);
   const uploader = isUploader(change, account);
   const reviewer = isReviewer(change, account);
-  return owner || uploader || reviewer;
+  const cc = isCc(change, account);
+  return owner || uploader || reviewer || cc;
 }
 
 export function getCurrentRevision(change?: ChangeInfo) {
diff --git a/polygerrit-ui/app/utils/common-util_test.js b/polygerrit-ui/app/utils/common-util_test.js
index 917d652b..d6d66d7 100644
--- a/polygerrit-ui/app/utils/common-util_test.js
+++ b/polygerrit-ui/app/utils/common-util_test.js
@@ -29,7 +29,7 @@
       assert.isTrue(hasOwnProperty(obj, 'name with spaces'));
       assert.isFalse(hasOwnProperty(obj, 'def'));
     });
-    test('object prototype has overriden hasOwnProperty', () => {
+    test('object prototype has overridden hasOwnProperty', () => {
       const F = function() {
         this.abc = 23;
       };
diff --git a/polygerrit-ui/app/utils/date-util.ts b/polygerrit-ui/app/utils/date-util.ts
index fad5041..3af8c59 100644
--- a/polygerrit-ui/app/utils/date-util.ts
+++ b/polygerrit-ui/app/utils/date-util.ts
@@ -37,9 +37,13 @@
 
 // similar to fromNow from moment.js
 export function fromNow(date: Date, noAgo = false) {
-  const now = new Date();
+  return durationString(date, new Date(), noAgo);
+}
+
+// similar to fromNow from moment.js
+export function durationString(from: Date, to: Date, noAgo = false) {
   const ago = noAgo ? '' : ' ago';
-  const secondsAgo = Math.floor((now.valueOf() - date.valueOf()) / 1000);
+  const secondsAgo = Math.floor((to.valueOf() - from.valueOf()) / 1000);
   if (secondsAgo <= 59) return 'just now';
   if (secondsAgo <= 119) return `1 minute${ago}`;
   const minutesAgo = Math.floor(secondsAgo / 60);
diff --git a/polygerrit-ui/app/utils/dom-util.ts b/polygerrit-ui/app/utils/dom-util.ts
index 32014d7..7f9ef72 100644
--- a/polygerrit-ui/app/utils/dom-util.ts
+++ b/polygerrit-ui/app/utils/dom-util.ts
@@ -156,7 +156,7 @@
 
 export function windowLocationReload() {
   const e = new Error();
-  console.info(`Calling window.location.realod(): ${e.stack}`);
+  console.info(`Calling window.location.reload(): ${e.stack}`);
   window.location.reload();
 }
 
diff --git a/polygerrit-ui/app/utils/label-util.ts b/polygerrit-ui/app/utils/label-util.ts
index 60ac4d8..4eed0a0 100644
--- a/polygerrit-ui/app/utils/label-util.ts
+++ b/polygerrit-ui/app/utils/label-util.ts
@@ -51,3 +51,11 @@
 ): ApprovalInfo | undefined {
   return label.all?.filter(x => x._account_id === account._account_id)[0];
 }
+
+export function labelCompare(labelName1: string, labelName2: string) {
+  if (labelName1 === CODE_REVIEW && labelName2 === CODE_REVIEW) return 0;
+  if (labelName1 === CODE_REVIEW) return -1;
+  if (labelName2 === CODE_REVIEW) return 1;
+
+  return labelName1.localeCompare(labelName2);
+}
diff --git a/polygerrit-ui/app/utils/label-util_test.js b/polygerrit-ui/app/utils/label-util_test.js
index 6a2f768..f9a30df 100644
--- a/polygerrit-ui/app/utils/label-util_test.js
+++ b/polygerrit-ui/app/utils/label-util_test.js
@@ -21,6 +21,7 @@
   getVotingRangeOrDefault,
   getMaxAccounts,
   getApprovalInfo,
+  labelCompare,
 } from './label-util.js';
 
 const VALUES_1 = {
@@ -113,4 +114,11 @@
     };
     assert.isUndefined(getApprovalInfo(label, myAccountInfo));
   });
+
+  test('labelCompare', () => {
+    let sorted = ['c', 'b', 'a'].sort(labelCompare);
+    assert.sameOrderedMembers(sorted, ['a', 'b', 'c']);
+    sorted = ['b', 'a', 'Code-Review'].sort(labelCompare);
+    assert.sameOrderedMembers(sorted, ['Code-Review', 'a', 'b']);
+  });
 });
diff --git a/polygerrit-ui/app/utils/patch-set-util.ts b/polygerrit-ui/app/utils/patch-set-util.ts
index 40e3eef..af56798 100644
--- a/polygerrit-ui/app/utils/patch-set-util.ts
+++ b/polygerrit-ui/app/utils/patch-set-util.ts
@@ -3,11 +3,12 @@
   ChangeInfo,
   PatchSetNum,
   EditPatchSetNum,
-  BrandType,
   ParentPatchSetNum,
+  PatchSetNumber,
 } from '../types/common';
 import {RestApiService} from '../services/gr-rest-api/gr-rest-api';
 import {EditRevisionInfo, ParsedChangeInfo} from '../types/types';
+import {check} from './common-util';
 
 /**
  * @license
@@ -82,9 +83,7 @@
   return patchset as PatchSetNum;
 }
 
-export function isNumber(
-  psn: PatchSetNum
-): psn is BrandType<number, '_patchSet'> {
+export function isNumber(psn: PatchSetNum): psn is PatchSetNumber {
   return typeof psn === 'number';
 }
 
@@ -250,14 +249,16 @@
 
 export function computeLatestPatchNum(
   allPatchSets?: PatchSet[]
-): PatchSetNum | undefined {
+): PatchSetNumber | undefined {
   if (!allPatchSets || !allPatchSets.length) {
     return undefined;
   }
-  if (allPatchSets[0].num === EditPatchSetNum) {
-    return allPatchSets[1].num;
+  let latest = allPatchSets[0].num;
+  if (latest === EditPatchSetNum) {
+    latest = allPatchSets[1].num;
   }
-  return allPatchSets[0].num;
+  check(isNumber(latest), 'Latest patchset cannot be EDIT or PARENT.');
+  return latest;
 }
 
 export function computePredecessor(
diff --git a/polygerrit-ui/app/utils/url-util_test.js b/polygerrit-ui/app/utils/url-util_test.js
index 0658be3..b1b17f4 100644
--- a/polygerrit-ui/app/utils/url-util_test.js
+++ b/polygerrit-ui/app/utils/url-util_test.js
@@ -25,15 +25,15 @@
 
 suite('url-util tests', () => {
   suite('getBaseUrl tests', () => {
-    let originialCanonicalPath;
+    let originalCanonicalPath;
 
     suiteSetup(() => {
-      originialCanonicalPath = window.CANONICAL_PATH;
+      originalCanonicalPath = window.CANONICAL_PATH;
       window.CANONICAL_PATH = '/r';
     });
 
     suiteTeardown(() => {
-      window.CANONICAL_PATH = originialCanonicalPath;
+      window.CANONICAL_PATH = originalCanonicalPath;
     });
 
     test('getBaseUrl', () => {
diff --git a/polygerrit-ui/app/yarn.lock b/polygerrit-ui/app/yarn.lock
index e544dbc..ec3b7a0 100644
--- a/polygerrit-ui/app/yarn.lock
+++ b/polygerrit-ui/app/yarn.lock
@@ -324,6 +324,11 @@
   dependencies:
     "@webcomponents/shadycss" "^1.9.1"
 
+"@types/resize-observer-browser@^0.1.5":
+  version "0.1.5"
+  resolved "https://registry.yarnpkg.com/@types/resize-observer-browser/-/resize-observer-browser-0.1.5.tgz#36d897708172ac2380cd486da7a3daf1161c1e23"
+  integrity sha512-8k/67Z95Goa6Lznuykxkfhq9YU3l1Qe6LNZmwde1u7802a3x8v44oq0j91DICclxatTr0rNnhXx7+VTIetSrSQ==
+
 "@webcomponents/shadycss@^1.9.1", "@webcomponents/shadycss@^1.9.2":
   version "1.9.4"
   resolved "https://registry.yarnpkg.com/@webcomponents/shadycss/-/shadycss-1.9.4.tgz#4f9d8ea1526bab084c60b53d4854dc39fdb2bb48"
diff --git a/proto/cache.proto b/proto/cache.proto
index 4fd037d..874e60a 100644
--- a/proto/cache.proto
+++ b/proto/cache.proto
@@ -524,13 +524,14 @@
 }
 
 // Serialized form of a list of com.google.gerrit.extensions.common.ContextLineInfo
-// Next ID: 2
+// Next ID: 3
 message AllCommentContextProto {
   message CommentContextProto {
     int32 line_number = 1;
     string context_line = 2;
   }
   repeated CommentContextProto context = 1;
+  string content_type = 2;
 }
 
 // Serialized key for
@@ -617,7 +618,7 @@
 
 // Serialized form of
 // com.google.gerrit.server.patch.filediff.FileDiffOutput
-// Next ID: 9
+// Next ID: 12
 message FileDiffOutputProto {
   // Next ID: 5
   message Edit {
@@ -632,6 +633,11 @@
     Edit edit = 1;
     bool due_to_rebase = 2;
   }
+  // Next ID: 3
+  message ComparisonType {
+    int32 parent_num = 1;
+    bool auto_merge = 2;
+  }
   string old_path = 1;
   string new_path = 2;
   string change_type = 3;
@@ -640,4 +646,7 @@
   int64 size = 6;
   int64 size_delta = 7;
   repeated TaggedEdit edits = 8;
+  bytes old_commit = 9;
+  bytes new_commit = 10;
+  ComparisonType comparison_type = 11;
 }
diff --git a/tools/bzl/maven_jar.bzl b/tools/bzl/maven_jar.bzl
index 15b1797..d96ffc2 100644
--- a/tools/bzl/maven_jar.bzl
+++ b/tools/bzl/maven_jar.bzl
@@ -60,7 +60,7 @@
     if len(parts) == 3:
         group_id, artifact_id, version = parts
     elif len(parts) == 4:
-        group_id, artifact_id, version, packaging = parts
+        group_id, artifact_id, version, classifier = parts
     elif len(parts) == 5:
         group_id, artifact_id, version, packaging, classifier = parts
     else:
@@ -158,7 +158,10 @@
     srcjar = None
     if ctx.attr.src_sha1 or ctx.attr.attach_source:
         srcjar = jar + "-src.jar"
-        srcurl = url + "-sources.jar"
+        srcurl = url
+        if coordinates.classifier != None:
+            srcurl = url.replace("-" + coordinates.classifier, "")
+        srcurl += "-sources.jar"
         srcjar_path = ctx.path("jar/" + srcjar)
         args = [python, script, "-o", srcjar_path, "-u", srcurl]
         if ctx.attr.src_sha1:
diff --git a/tools/remote-bazelrc b/tools/remote-bazelrc
index de7d0df..22ee330 100644
--- a/tools/remote-bazelrc
+++ b/tools/remote-bazelrc
@@ -42,9 +42,6 @@
 # Set various strategies so that all actions execute remotely. Mixing remote
 # and local execution will lead to errors unless the toolchain and remote
 # machine exactly match the host machine.
-build:remote --spawn_strategy=remote,sandboxed
-build:remote --strategy=Javac=remote
-build:remote --strategy=Genrule=remote
 build:remote --define=EXECUTOR=remote
 
 # Enable the remote cache so action results can be shared across machines,
@@ -68,6 +65,3 @@
 build:remote-cache --tls_enabled=true
 build:remote-cache --remote_timeout=3600
 build:remote-cache --auth_enabled=true
-build:remote-cache --spawn_strategy=standalone
-build:remote-cache --strategy=Javac=standalone
-build:remote-cache --strategy=Genrule=standalone