diff --git a/Documentation/backup.txt b/Documentation/backup.txt
new file mode 100644
index 0000000..cd247af
--- /dev/null
+++ b/Documentation/backup.txt
@@ -0,0 +1,270 @@
+= Gerrit Code Review - Backup
+
+A Gerrit Code Review site contains data that needs to be backed up regularly.
+This document describes best practices for backing up review data.
+
+[#mand-backup]
+== Data which must be backed up
+
+[#mand-backup-git]
+Git repositories::
++
+The bare Git repositories managed by Gerrit are typically stored in the
+`${SITE}/git` directory. However, the locations can be customized in
+`${site}/etc/gerrit.config`. They contain the history of the respective
+projects, and since 2.15 if you are using _NoteDb_, and for 3.0 and newer,
+also change and review metadata, user accounts and groups.
++
+
+[#mand-backup-db]
+SQL database::
++
+Gerrit releases in the 2.x series store some data in the database you
+have chosen when installing Gerrit. If you are using 2.16 and have
+migrated to _NoteDb_ only the schema version is stored in the database.
++
+If you are using h2 you need to backup the `.db` files in the folder
+`${SITE}/db`.
++
+For all other database types refer to their backup documentation.
++
+Gerrit release 3.0 and newer store all primary data in _NoteDb_ inside
+the git repositories of the Gerrit site. Only the review flag marking in
+the UI when you have reviewed a changed file is stored in a relational
+database. If you are using h2 this database is named
+`account_patch_reviews.h2.db`.
+
+[#optional-backup]
+== Data optional to be backed up
+
+[#data-optional-backup-index]
+Search index::
++
+The _Lucene_ search index is stored in the `${SITE}/index` folder.
+It can be recomputed from primary data in the git repositories but
+reindexing may take a long time hence backing up the index makes sense
+for production installations.
++
+If you have chosen to use _Elastic Search_ for indexing,
+refer to its
+link:https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-snapshots.html[backup documentation].
+
+[#optional-backup-cache]
+Caches::
++
+Gerrit uses many caches which populate automatically. Some of the caches
+are persisted in the directory `${SITE}/cache` to retain the cached data
+across restarts. Since repopulating persistent caches takes time and server
+resources it makes sense to include them in backups to avoid unnecessary
+higher load and degraded performance when a Gerrit site has been restored
+from backup and caches need to be repopulated.
+
+[#optional-backup-config]
+Configuration::
++
+Gerrit configuration files are located in the directory `${SITE}/etc`
+and should be backed up or versioned in a git repository. The `etc`
+directory also contains secrets which should be handled separately
++
+* `secure.config` contains passwords and `auth.registerEmailPrivateKey`
+* public and private SSH host keys
++
+You may consider to use the
+link:https://gerrit.googlesource.com/plugins/secure-config/[secure-config plugin]
+to encrypt these secrets.
+
+[#optional-backup-plugin-data]
+Plugin Data::
++
+The `${SITE}/data/` directory is used by plugins storing data like e.g.
+the delete-project and the replication plugin.
+
+[#optional-backup-libs]
+Libraries::
++
+The `${SITE}/lib/` directory contains libraries used as statically loaded
+plugin or providing additional dependencies needed by Gerrit plugins.
+
+[#optional-backup-plugins]
+Plugins::
++
+The `${SITE}/plugins/` directory contains the installed Gerrit plugins.
+
+[#optional-backup-static]
+Static Resources::
++
+The `${SITE}/static/` directory contains static resources used to customize the
+Gerrit UI and email templates.
+
+[#optional-backup-logs]
+Logs::
++
+The `${SITE}/logs/` directory contains Gerrit server log files. Logs can still
+be written when the server is in read-only mode.
+
+[#cons-backup]
+== Consistent backups
+
+There are several ways to ensure consistency when backing up primary data.
+
+[#cons-backup-snapshot]
+=== Filesystem snapshots
+
+Gerrit 3.0 or newer::
++
+* all primary data is stored in git
+* Use a file system like lvm, zfs, btrfs or nfs supporting snapshots.
+Create a snapshot and then archive the snapshot.
+
+Gerrit 2.x::
++
+Gerrit 2.16 can use _NoteDb_ to store almost all this data which
+simplifies creating backups since consistency between database and git
+repositories is no longer critical. If you migrated to _NoteDb_ you can
+follow the backup procedure for 3.0 and higher and additionally take
+a backup of the database, which only contains the schema version,
+hence consistency between git and database is no longer critical since
+the schema version only changes during upgrade. If you didn't migrate
+to _NoteDb_ then follow the backup procedure for older 2.x Gerrit versions.
++
+Older 2.x Gerrit versions store change meta data, review comments, votes,
+accounts and group information in a SQL database. Creating consistent backups
+where git repositories and the data stored in the database are backed up
+consistently requires to turn the server read-only or to shut it down
+while creating the backup since there is no integrated transaction handling
+between git repositories and the SQL database. Also crons and currently
+running cron jobs (e.g. repacking repositories) which affect the repositories
+may need to be shut down.
+Use a file system supporting snapshots to keep the period where the gerrit
+server is read-only or down as short as possible.
+
+[#cons-backup-read-only]
+=== Turn master read-only for backup
+
+Make the server read-only before taking the backup. This means read-access
+is still available during backup, because only write operations have to be
+stopped to ensure consistency. This can be implemented using the
+link:https://gerrit.googlesource.com/plugins/readonly/[_readonly_] plugin.
+
+[#cons-backup-replicate]
+=== Replicate data for backup
+
+Replicating the git repositories can backup the most critical repository data
+but does not backup repository meta-data such as the project description
+file, ref-logs, git configs, and alternate configs.
+
+Replicate all git repositories to another file system using
+`git clone --mirror`,
+or the
+link:https://gerrit.googlesource.com/plugins/replication[replication plugin]
+or the
+link:https://gerrit.googlesource.com/plugins/pull-replication[pull-replication plugin].
+Best you use a filesystem supporting snapshots to create a backup archive
+of such a replica.
+
+For 2.x Gerrit versions also set up a database replica for the data stored in the
+SQL database. If you are using 2.16 and migrated to _NoteDb_ you may consider to
+skip setting up a database replica, instead take a backup of the database which only
+contains the current schema version in this case.
+In addition you need to ensure that no write operations are in flight before you
+take the replica offline. Otherwise the database backup might be inconsistent
+with the backup of the git repositories.
+
+Do not skip backing up the replica, the replica alone IS NOT a backup.
+Imagine someone deleted a project by mistake and this deletion got replicated.
+Replication of repository deletions can be switched off using the
+link:https://gerrit.googlesource.com/plugins/replication/+/refs/heads/master/src/main/resources/Documentation/config.md[server option]
+`remote.NAME.replicateProjectDeletions`.
+
+If you are using Gerrit replica to offload read traffic you can use one of these
+replica for creating backups.
+
+[#cons-backup-offline]
+=== Take master offline for backup
+
+Shutdown the server before taking a backup. This is simple but means downtime
+for the users. Also crons and currently running cron jobs (e.g. repacking
+repositories) which affect the repositories may need to be shut down.
+
+[#backup-methods]
+== Backup methods
+
+[#backup-methods-snapshots]
+=== Filesystem snapshots
+
+Filesystems supporting copy on write snapshots::
++
+Use a file system supporting copy-on-write snapshots like
+link:https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Snapshots[btrfs]
+or
+https://wiki.debian.org/ZFS#Snapshots[zfs].
+
+
+Other filesystems supporting snapshots::
+https://wiki.archlinux.org/index.php/LVM#Snapshots[lvm] or nfs.
++
+Create a snapshot and then archive the snapshot to another storage.
++
+While snapshots are great for creating high quality backups quickly, they are
+not ideal as a format for storing backup data. Snapshots typically depend and
+reside on the same storage infrastructure as the original disk images.
+Therefore, it’s crucial that you archive these snapshots and store them
+elsewhere.
+
+3.0 or newer::
+Snapshot the complete site directory
+
+2.x::
+Similar, but the data of the database should be stored on the very same volume
+on the same machine, so that the snapshot is taken atomically over both
+the git data and the database data. Because everything should be ACID, it can safely
+crash-recover - as if the power has been plugged and the server got booted up again.
+(Actually more safe than that, because the filesystem knows about taking the snapshot,
+and also about the pending writes it can sync.)
+
+In addition to that, using filesystem snapshots allows to:
+
+* easy and fast roll back without having to access remote backup data (e.g. to restore
+accidental rm -rf git/ back in seconds).
+* incremental transfer of consistent snapshots
+* save a lot of data while still keeping multiple "known consistent states"
+
+[#backup-methods-other]
+=== Other backup methods
+
+To ensure consistent backups these backup methods require to turn the server into
+read-only mode while a backup is running.
+
+* create an archive like `tar.gz` to backup the site
+* `rsync`
+* plain old `cp`
+
+[#backup-methods-test]
+== Test backups
+
+Test backups and fire drill restoring backups to ensure the backups aren't
+corrupt or incomplete and you can restore a backup quickly.
+
+[#backup-dr]
+== Disaster recovery
+
+[#backup-dr-repl]
+=== Replicate backup archives
+
+To enable disaster recovery at least replicate backup archives to another data center.
+And fire drill restoring a new site using the backup.
+
+[#backup-dr-multi-site]
+=== Multi-site setup
+
+Use the https://gerrit.googlesource.com/plugins/multi-site[multi-site plugin]
+to install Gerrit with multiple sites installed in different datacenters
+across different regions. This ensures that in case of a severe problem with
+one of the sites, the other sites can still serve your repositories.
+
+GERRIT
+------
+Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------
diff --git a/Documentation/dev-bazel.txt b/Documentation/dev-bazel.txt
index 925d399..436b918 100644
--- a/Documentation/dev-bazel.txt
+++ b/Documentation/dev-bazel.txt
@@ -304,6 +304,12 @@
   bazel test --test_tag_filters=-docker //...
 ----
 
+To exclude tests that require very recent git client version:
+
+----
+  bazel test --test_tag_filters=-git-protocol-v2 //...
+----
+
 To ignore cached test results:
 
 ----
@@ -324,6 +330,7 @@
 * edit
 * elastic
 * git
+* git-protocol-v2
 * notedb
 * pgm
 * rest
diff --git a/Documentation/images/user-review-ui-change-complex-reply-dialogue.png b/Documentation/images/user-review-ui-change-complex-reply-dialogue.png
new file mode 100644
index 0000000..1286852
--- /dev/null
+++ b/Documentation/images/user-review-ui-change-complex-reply-dialogue.png
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diff --git a/Documentation/images/user-review-ui-change-page-download.png b/Documentation/images/user-review-ui-change-page-download.png
new file mode 100644
index 0000000..63c4ee3
--- /dev/null
+++ b/Documentation/images/user-review-ui-change-page-download.png
Binary files differ
diff --git a/Documentation/images/user-review-ui-change-page-patchset-dropdown.png b/Documentation/images/user-review-ui-change-page-patchset-dropdown.png
new file mode 100644
index 0000000..f71473e
--- /dev/null
+++ b/Documentation/images/user-review-ui-change-page-patchset-dropdown.png
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diff --git a/Documentation/images/user-review-ui-change-relation-chain.png b/Documentation/images/user-review-ui-change-relation-chain.png
new file mode 100644
index 0000000..19942f1
--- /dev/null
+++ b/Documentation/images/user-review-ui-change-relation-chain.png
Binary files differ
diff --git a/Documentation/images/user-review-ui-change-reply-dialogue.png b/Documentation/images/user-review-ui-change-reply-dialogue.png
new file mode 100644
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--- /dev/null
+++ b/Documentation/images/user-review-ui-change-reply-dialogue.png
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diff --git a/Documentation/index.txt b/Documentation/index.txt
index 77e0ed4..63671cd 100644
--- a/Documentation/index.txt
+++ b/Documentation/index.txt
@@ -9,6 +9,7 @@
 . link:intro-quick.html[Product Overview]
 . link:intro-how-gerrit-works.html[How Gerrit Works]
 . link:intro-gerrit-walkthrough.html[Basic Gerrit Walkthrough]
+.. link:intro-gerrit-walkthrough-github.html[Basic Gerrit Walkthrough -- For GitHub Users]
 . link:dev-community.html[Gerrit Community]
 .. link:dev-contributing.html[Contributor Guide]
 
diff --git a/Documentation/install.txt b/Documentation/install.txt
index 2b6cc6e..fe32029 100644
--- a/Documentation/install.txt
+++ b/Documentation/install.txt
@@ -249,6 +249,11 @@
 * http://www.kernel.org/pub/software/scm/git/docs/git-daemon.html[git-daemon]
 
 
+[[backup]]
+== Backup
+
+See the link:backup.html[backup documentation].
+
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]
diff --git a/Documentation/intro-gerrit-walkthrough-github.txt b/Documentation/intro-gerrit-walkthrough-github.txt
new file mode 100644
index 0000000..39a779d
--- /dev/null
+++ b/Documentation/intro-gerrit-walkthrough-github.txt
@@ -0,0 +1,263 @@
+= Basic Gerrit Walkthrough -- For GitHub Users
+
+
+[NOTE]
+====
+This document aims to provide a concise description of the core principles of
+code review in Gerrit for people that were previously using Pull Requests on
+Github or similar concepts. Nothing in this document is meant to state that
+one or the other might be better, but only aims to help new users understand
+Gerrit more readily. We use Github as the point of comparison since it seems
+to be the most popular service.
+====
+
+To illustrate the differences in a meaningful order, we will walk you through
+the process of cloning a repo, making a change, asking for code review,
+iterating on the code and finally having it submitted to the code base. This
+document also does not aim to describe all features of Gerrit. Please refer to
+the link:intro-gerrit-walkthrough.html[Basic Gerrit Walkthrough] or
+link:index.html[the rest of the documentation] for a more complete overview and additional pointers.
+
+[[tldr]]
+== tl;dr
+
+Here’s how getting code reviewed and submitted with Gerrit is different from
+doing the same with GitHub:
+
+* You need the add a commit-msg hook script when you clone a repo for the first
+time using a snippet you can find e.g. https://gerrit-review.googlesource.com/admin/repos/gerrit[here];
+* Your review will be on a single commit instead of a branch. You use
+`git commit --amend` to modify a code change.
+* Instead of using the Web UI to create a pull request, you use
+`git push origin HEAD:refs/for/master` to upload new local commits that are
+ready for review to Gerrit. You will find the URL to the review in the output of
+the push command.
+* As a reviewer, Gerrit offers a number of so-called labels to vote on, one of
+which is Code-Review. You indicate a negative, neutral or positive review using
+a -1, 0 or +1 vote.
+* To be able to submit (== merge) a change, you usually need a +2 Code-Review
+vote and possibly additional positive votes, depending on the configuration of
+the project you are contributing to.
+
+[[clone]]
+== 1. Cloning a Repository
+
+[NOTE]
+====
+Both GitHub and Gerrit provide simple Git repository hosting (of course both can
+do much more). In the simplest setup, you could just use both as such without
+any code review to push code. We will assume that this is not what you want to
+do and focus on the use case where your change requires a review.
+====
+
+The first step to working with the code is to clone the repo. For both, Gerrit
+and GitHub, you can simply use the `git clone` command.
+
+For Gerrit, there is an additional step before you can start making changes. For
+reasons we explain below, you’ll have to add a https://gerrit-review.googlesource.com/Documentation/user-changeid.html[commit-msg hook] script. This will
+append the Gerrit Change-Id to every commit message such that Gerrit can track
+commits through the review process. To make this process a little easier in
+Gerrit, you can find a command snippet for cloning and adding the commit-msg
+hook on the repository page (e.g. https://gerrit-review.googlesource.com/admin/repos/gerrit[here]).
+
+[[create-change]]
+== 2. Making a Change
+
+*Branches*
+
+Now that you have the code in the git repo on your machine, you can start making
+changes. With GitHub, you would usually create a new branch and then start
+committing to it. This branch would then contain all the changes you share with
+your code reviewers in the next step. Your local branch will usually also be
+pushed to the remote server. This can be handy to back up your work or hand-off
+work to another device or developer.
+
+With Gerrit, you can also create a new local branch to develop in. While not
+required, it can be considered a best practice to sandbox this change from other
+changes you might be making. In contrast to the GitHub model, your local branch
+will not have to be pushed to the remote in Gerrit, at least not for the
+purposes of code review.
+
+*Commits*
+In Gerrit, a single commit is the unit of code that will be reviewed. With
+GitHub, you can commit to your branch as much as you like and the sum of all
+your commits on that branch will get reviewed. As a single commit gets reviewed
+in Gerrit, you need to `git commit --amend` when you iterate on the same change as
+opposed to only using `git commit` with GitHub (see Section 5 for more). You can,
+however, also add another commit on top of your existing commit in Gerrit, which
+will create a second change (and thus another review) that is based on your
+first change. Gerrit will show the relationship between these two changes as a
+so-called relation chain. This also means that your second change can only be
+submitted after the first was successfully merged. In many basic use cases, this
+situation is however not what you want.
+
+image::images/user-review-ui-change-relation-chain.png[Relation chain display on the change page.]
+
+With GitHub, you may be pushing your branch to the remote for non-code-review
+purposes, as mentioned above. You usually do not do this with Gerrit, as
+Gerrit-managed repos often only have one or a few branches on the server that
+can only be merged into via code review.
+
+[[request-review]]
+== 3. Asking for Code Review
+
+After you are satisfied with the changes you made, you’ll usually want/need to
+get your code reviewed. In GitHub, you would push your branch to the remote, go
+to the Web UI and create a pull request. In Gerrit, you need to push your commit
+(or the series of changes/commits) to the remote first, since you usually
+develop in a local branch only. While you can often just use git push with
+GitHub, you need to do a slightly different thing for Gerrit. Gerrit uses a
+“magic” branch that tells the server that this code is supposed to be reviewed.
+To send the changes you made on your local branch to review and being eventually
+merged into the remote’s master branch, you use
+`git push origin HEAD:refs/for/master`. There are also link:user-upload.html#_git_push[a number of Gerrit change
+options] you can trigger from the CLI this way.
+
+After successfully pushing your change to Gerrit, you will already find the URL
+for viewing your change in Gerrit’s Web UI in the response you get from the
+server. The description of the Gerrit code review that was just created is equal
+to the commit message of that one commit the change is based on. In GitHub, you
+might have described your change in the message you can create when creating the
+pull request in the GitHub Web UI.
+
+Next, you would go and visit your Gerrit change in the Web UI to get your change
+ready for review (choose reviewers, cc people, check for failing CI builds or
+tests, etc.), very similar to what you do on Github. Reviewers will be notified
+via email once you add them. By default, anyone can add reviewers to a Gerrit
+change. In GitHub, this ability is reserved for certain users, so you may have
+relied on others adding reviewers for you before. This can be the case in a
+Gerrit project, but it is also often expected that the change owner (usually the
+creator of the change) adds reviewers to get the review process started.
+
+[[reviewing]]
+== 4. Reviewing a Change
+
+Switching perspectives briefly, reviewing a change is fairly similar between
+GitHub and Gerrit. You, as a reviewer, will be notified of a change you have
+been added to via email or see an “incoming” change on your Gerrit dashboard.
+The dashboard is the central overview of changes going on within a Gerrit
+instance. By default, the dashboard shows changes that you are involved in, in
+any way. You can also see all changes on a Gerrit server by using the top menu
+(“Changes” -> “Open”). This view is more similar to what you see on Github, when
+you navigate to the Pull Requests tab of the project/repository you are working
+on. Note, however, that a single Gerrit instance can host multiple projects
+(also referred to as repositories; a list can be found, for example, https://gerrit-review.googlesource.com/admin/repos[here]). Your
+dashboard and other lists of changes will show all changes across the
+projects/repositories by default.
+
+Back to your dashboard, you can click on the change you want to review. You can
+also access this from the email you received. You will see the same view that
+you saw as an author. In the middle of the change page, you can find the list of
+files that have been modified, just like what you find in the “Files changed”
+tab of GitHub. Also similarly, you can leave comments by highlighting a piece of
+the code and pressing ‘c’. All comments you make are in a draft state and thus
+only visible to you, like on GitHub. When you are done with your review, you
+need to click the “Reply” button at the top of the change page to send your
+assessment to the change owner alongside a “change message” summarizing your
+findings and/or adding higher level comments. Replying to a change makes your
+draft comments and the change message visible on the change page for everyone
+that has view access to this change. This again is fairly similar to GitHub,
+except for Gerrit’s voting labels.
+
+image::images/user-review-ui-change-reply-dialogue.png[Reply dialogue for a Gerrit change.]
+
+As you can see in the screenshot of the reply dialogue, the voting labels are in
+the bottom part of the dialogue. They can be fairly simple as in this case, but
+there can also be a larger number of labels you might be able to vote on. Labels
+can be used to distinguish different aspects of a review (e.g. whether or not
+the licensing of included libraries is okay), outcome of CI systems (e.g.
+whether or not a format checker passed, a build completed successfully, etc.) or
+as a flag that is read by bots to do something with a change. An example of a
+more complex label setup can be seen in this screenshot from the Android Gerrit
+instance.
+
+image::images/user-review-ui-change-complex-reply-dialogue.png[Reply dialogue for a change on the Android project.]
+
+In the simplest case shown above, voting -1 on the Code-Review label equals
+requesting changes on a GitHub pull request, 0 equals just having comments and
++1 means that you think this change looks good. Usually, Gerrit changes require
+a +2 vote on the Code-Review label to be submitted (merged in GitHub terms, see
+Section 6 below). Being able to vote +2 on Code-Review is often restricted to
+maintainers of a given project, so they can have a final say on a change. These
+practices can however vary between projects, as labels and voting permissions
+are configurable.
+
+[[iterate]]
+== 5. Iterating on the Change
+
+After your reviewers got back to you as a change owner, you realize that you
+need to make a few updates to the code in your change. As mentioned in Section 2
+(Making a Change), you’ll have to amend the commit that this review was based
+on. To do that, you might have to checkout the respective commit first if it is
+not at the tip of your local branch, for example if you stacked multiple changes
+on top of each other. Another common use case is to not have a local branch but
+to work in the so-called https://www.git-tower.com/learn/git/faq/detached-head-when-checkout-commit["detached HEAD"] mode. In that case you can use the
+“Download” button on the files tab to copy a command that fetches and checks out
+the commit underlying your change. Make sure to select the latest patchset,
+though!
+
+image::images/user-review-ui-change-page-download.png[Using the “Download” button to copy a command that checks out a given patchset for a change.]
+
+After checking out the commit, you then make the changes as usual. When you
+think you are done, you can commit with the `--amend` flag to change the commit
+you currently have checked out.
+
+When you `git commit --amend` to iterate on your change, you might be worried that
+you are changing your previous commit and may thus lose that state of your work.
+However, here the Change-Id appended to your commit message comes into play.
+While the SHA1 hash of your change (the commit ID used by Git) might change, the
+Change-Id stays the same (in fact it is the SHA1 hash of the very first version
+of that commit). When this amended commit is uploaded to the Gerrit server,
+Gerrit knows that this commit is really an iteration of that previous commit
+(and the associated review) and will preserve both, the old and the new state.
+All previous states of your commit will be visible in the Gerrit UI as so-called
+patchsets (and link:intro-user.html#change-ref[from the Git repo]).
+
+image::images/user-review-ui-change-page-patchset-dropdown.png[Screenshot of the patchset dropdown above the file list, showing all iterations a commit went through.]
+
+After iterating as much as needed, your reviewers will finally be satisfied.
+With GitHub, you would have a string of additional commits in the branch you
+used for opening the pull request. In Gerrit, you still only have that one
+commit in your local branch. All the iterations are available as patchsets in
+the Web UI as well as from the special branch mentioned above.
+
+[[submit]]
+== 6. Submitting a Change
+
+Finally, it is time to submit your change. As mentioned above, the precondition
+for this in Gerrit is usually at least a +2 vote on the Code-Review label. With
+GitHub, an authorized person must have given an “Approve” vote. Once this
+precondition has been met, anyone with submit permission can submit the change
+in Gerrit. To do that, you click the “Submit” button in the Gerrit Web UI just
+as you would click the “Merge Pull Request” button in GitHub. Both, Gerrit and
+GitHub, allow different merge strategies, that can be enabled by project
+administrators. In Gerrit, a merge strategy is configured for each project and
+cannot be changed at submit time while this may be possible with GitHub,
+depending on project configuration.
+
+A merge can fail due to conflicts with competing edits on the target branch.
+With GitHub, you may be able to resolve some simple conflicts directly from the
+Web UI. In Gerrit, you can attempt to rebase a change from the Web UI. If there
+are no conflicts, a new patchset will automatically appear. Otherwise, similar
+to GitHub, you need to resolve conflicts on the command line with your local
+clone of the repository. While you resolve conflicts that arise from a
+`git merge` for GitHub, you will need to link:intro-user.html#rebase[use `git rebase` with your change] on
+Gerrit.
+
+After resolving locally, with GitHub, you end up with another commit on your
+pull request branch and push it to the server, which should then allow you to
+finish merging the change. With Gerrit, resolving the conflict through rebasing
+your commit/change results in another amended version of that same commit and
+you upload it to Gerrit, resulting in a new patchset just like your previous
+iterations addressing reviewer comments. This new patchset will usually require
+another round of reviewer votes, as Gerrit will not copy votes from a previous
+patchset by default.
+
+
+GERRIT
+------
+
+Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------
diff --git a/Documentation/intro-user.txt b/Documentation/intro-user.txt
index b13ae83..16929ae 100644
--- a/Documentation/intro-user.txt
+++ b/Documentation/intro-user.txt
@@ -538,7 +538,9 @@
 ----
   $ git push origin HEAD:refs/for/master%wip
 ----
-Alternatively, click *WIP* from the Change screen.
+Alternatively, click *WIP* from the *More* menu on the Change screen.
+The Change screen updates with a yellow header, indicating that
+the change is in a Work-in-Progress state.
 
 To mark the change as ready for review, append `%ready` to your push
 request.
@@ -546,18 +548,12 @@
 ----
   $ git push origin HEAD:refs/for/master%ready
 ----
-Alternatively, click *Ready* from the Change screen.
+Alternatively, click *Start Review* from the Change screen.
 
 Change owners, project owners, site administrators and members of a group that
 was granted "Toggle Work In Progress state" permission can mark changes as
 `work-in-progress` and `ready`.
 
-[[wip-polygerrit]]
-In the new PolyGerrit UI, you can mark a change as WIP, by selecting *WIP* from
-the *More* menu. The Change screen updates with a yellow header, indicating that
-the change is in a Work-in-Progress state. To mark a change as ready for review,
-click *Start Review*.
-
 [[private-changes]]
 == Private Changes
 
diff --git a/Documentation/js-api.txt b/Documentation/js-api.txt
index 030541d..893ab36 100644
--- a/Documentation/js-api.txt
+++ b/Documentation/js-api.txt
@@ -150,6 +150,13 @@
 parameter the URL of the plugin is returned. If passed a string
 the argument is appended to the plugin URL.
 
+A plugin's URL is where this plugin is loaded, it doesn't
+necessary to be the same as the Gerrit host. Use `window.location`
+if you need to access the Gerrit host info.
+
+For preloaded plugins, the plugin url is based on a global
+configuration of where to load all plugins, default to current host.
+
 [source,javascript]
 ----
 self.url();                    // "https://gerrit-review.googlesource.com/plugins/demo/"
diff --git a/Jenkinsfile b/Jenkinsfile
index f21c7897..988f839 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -88,6 +88,10 @@
     }
 }
 
+def hasChangeNumber() {
+    env.GERRIT_CHANGE_NUMBER?.trim()
+}
+
 def postCheck(check) {
     def gerritPostUrl = Globals.gerritUrl +
         "a/changes/${check.changeNum}/revisions/${check.sha1}/checks"
@@ -185,17 +189,17 @@
 
 def collectBuilds() {
     def builds = [:]
-    if (env.GERRIT_CHANGE_NUMBER == "") {
+    if (hasChangeNumber()) {
+       builds["Gerrit-codestyle"] = prepareBuildsForMode("Gerrit-codestyle")
+       Builds.modes.each {
+          builds["Gerrit-verification(${it})"] = prepareBuildsForMode("Gerrit-verifier-bazel", it)
+       }
+    } else {
        builds["java8"] = { -> build "Gerrit-bazel-${env.BRANCH_NAME}" }
 
        if (env.BRANCH_NAME == "master") {
           builds["java11"] = { -> build "Gerrit-bazel-java11-${env.BRANCH_NAME}" }
        }
-    } else {
-        builds["Gerrit-codestyle"] = prepareBuildsForMode("Gerrit-codestyle")
-        Builds.modes.each {
-            builds["Gerrit-verification(${it})"] = prepareBuildsForMode("Gerrit-verifier-bazel", it)
-        }
     }
     return builds
 }
@@ -282,7 +286,7 @@
 
 node ('master') {
 
-    if (env.GERRIT_CHANGE_NUMBER != "") {
+    if (hasChangeNumber()) {
         stage('Preparing'){
             gerritReview labels: ['Verified': 0, 'Code-Style': 0]
 
@@ -293,7 +297,7 @@
 
     parallel(collectBuilds())
 
-    if (env.GERRIT_CHANGE_NUMBER != "") {
+    if (hasChangeNumber()) {
         stage('Retry Flaky Builds'){
             def flakyBuildsModes = findFlakyBuilds()
             if (flakyBuildsModes.size() > 0){
diff --git a/WORKSPACE b/WORKSPACE
index 307e28c..0804bec 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -32,9 +32,9 @@
 
 http_archive(
     name = "io_bazel_rules_closure",
-    sha256 = "0409f8bd2a8b6fd1db289cdc0acb394dafd69f60a86d0169bc6495e648e01587",
-    strip_prefix = "rules_closure-18f8acf24ae0d03a9c3ee872ff91dcfbf383d69e",
-    urls = ["https://github.com/bazelbuild/rules_closure/archive/18f8acf24ae0d03a9c3ee872ff91dcfbf383d69e.tar.gz"],
+    sha256 = "03c3b16f205085817fd89cfdcb2220a0138647ee7992be9cef291b069dd90301",
+    strip_prefix = "rules_closure-196a45f0ede2faec11dcc6c60fbc5e7471f4bd58",
+    urls = ["https://github.com/bazelbuild/rules_closure/archive/196a45f0ede2faec11dcc6c60fbc5e7471f4bd58.tar.gz"],
 )
 
 # File is specific to Polymer and copied from the Closure Github -- should be
diff --git a/java/com/google/gerrit/common/data/SubmitTypeRecord.java b/java/com/google/gerrit/common/data/SubmitTypeRecord.java
index d16da96..afb3bac 100644
--- a/java/com/google/gerrit/common/data/SubmitTypeRecord.java
+++ b/java/com/google/gerrit/common/data/SubmitTypeRecord.java
@@ -65,7 +65,7 @@
     StringBuilder sb = new StringBuilder();
     sb.append(status);
     if (status == Status.RULE_ERROR && errorMessage != null) {
-      sb.append('(').append(errorMessage).append(")");
+      sb.append(" (").append(errorMessage).append(")");
     }
     if (type != null) {
       sb.append('[');
diff --git a/java/com/google/gerrit/exceptions/InvalidMergeStrategyException.java b/java/com/google/gerrit/exceptions/InvalidMergeStrategyException.java
new file mode 100644
index 0000000..d9c5776
--- /dev/null
+++ b/java/com/google/gerrit/exceptions/InvalidMergeStrategyException.java
@@ -0,0 +1,23 @@
+// Copyright (C) 2019 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.exceptions;
+
+public class InvalidMergeStrategyException extends RuntimeException {
+  private static final long serialVersionUID = 1L;
+
+  public InvalidMergeStrategyException(String strategy) {
+    super("invalid merge strategy: " + strategy);
+  }
+}
diff --git a/java/com/google/gerrit/httpd/restapi/RestApiServlet.java b/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
index 0535397..bd32c0b 100644
--- a/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
+++ b/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
@@ -1670,18 +1670,37 @@
     if (!res.isCommitted()) {
       res.reset();
       traceContext.getTraceId().ifPresent(traceId -> res.addHeader(X_GERRIT_TRACE, traceId));
-      StringBuilder msg = new StringBuilder("Internal server error");
       ImmutableList<String> userMessages =
           globals.exceptionHooks.stream()
               .map(h -> h.getUserMessage(err))
               .filter(Optional::isPresent)
               .map(Optional::get)
               .collect(toImmutableList());
+
+      Optional<Integer> statusCode =
+          globals.exceptionHooks.stream()
+              .map(h -> h.getStatusCode(err))
+              .filter(Optional::isPresent)
+              .map(Optional::get)
+              .findFirst();
+      if (statusCode.isPresent() && statusCode.get() < 400) {
+        StringBuilder msg = new StringBuilder();
+        if (userMessages.size() == 1) {
+          msg.append(userMessages.get(0));
+        } else {
+          userMessages.forEach(m -> msg.append("\n* ").append(m));
+        }
+
+        res.setStatus(statusCode.get());
+        logger.atFinest().withCause(err).log("REST call finished: %d", statusCode.get().intValue());
+        return replyText(req, res, true, msg.toString());
+      }
+
+      StringBuilder msg = new StringBuilder("Internal server error");
       if (!userMessages.isEmpty()) {
-        msg.append("\n");
         userMessages.forEach(m -> msg.append("\n* ").append(m));
       }
-      return replyError(req, res, SC_INTERNAL_SERVER_ERROR, msg.toString(), err);
+      return replyError(req, res, statusCode.orElse(SC_INTERNAL_SERVER_ERROR), msg.toString(), err);
     }
     return 0;
   }
diff --git a/java/com/google/gerrit/pgm/Daemon.java b/java/com/google/gerrit/pgm/Daemon.java
index 568fb60..da8411f 100644
--- a/java/com/google/gerrit/pgm/Daemon.java
+++ b/java/com/google/gerrit/pgm/Daemon.java
@@ -538,14 +538,14 @@
 
   private Injector createWebInjector() {
     final List<Module> modules = new ArrayList<>();
-    if (sshd) {
-      modules.add(new ProjectQoSFilter.Module());
-    }
     modules.add(RequestContextFilter.module());
     modules.add(RequestMetricsFilter.module());
     modules.add(H2CacheBasedWebSession.module());
     modules.add(sysInjector.getInstance(GerritAuthModule.class));
     modules.add(sysInjector.getInstance(GitOverHttpModule.class));
+    if (sshd) {
+      modules.add(new ProjectQoSFilter.Module());
+    }
     modules.add(AllRequestFilter.module());
     modules.add(sysInjector.getInstance(WebModule.class));
     modules.add(sysInjector.getInstance(RequireSslFilter.Module.class));
diff --git a/java/com/google/gerrit/prettify/BUILD b/java/com/google/gerrit/prettify/BUILD
index 7c1241a..0a15fda 100644
--- a/java/com/google/gerrit/prettify/BUILD
+++ b/java/com/google/gerrit/prettify/BUILD
@@ -7,5 +7,7 @@
     deps = [
         "//lib:guava",
         "//lib:jgit",
+        "//lib/auto:auto-value",
+        "//lib/auto:auto-value-annotations",
     ],
 )
diff --git a/java/com/google/gerrit/prettify/common/SparseFileContent.java b/java/com/google/gerrit/prettify/common/SparseFileContent.java
index 348f9b2..1249b65 100644
--- a/java/com/google/gerrit/prettify/common/SparseFileContent.java
+++ b/java/com/google/gerrit/prettify/common/SparseFileContent.java
@@ -14,160 +14,175 @@
 
 package com.google.gerrit.prettify.common;
 
-import java.util.ArrayList;
-import java.util.List;
+import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableList;
 
-public class SparseFileContent {
-  protected List<Range> ranges;
-  protected int size;
+/**
+ * A class to store subset of a file's lines in a memory efficient way. Internally, it stores lines
+ * as a list of ranges. Each range represents continuous set of lines and has information about line
+ * numbers in original file (zero-based).
+ *
+ * <p>{@link SparseFileContent.Accessor} must be used to work with the stored content.
+ */
+@AutoValue
+public abstract class SparseFileContent {
+  abstract ImmutableList<Range> getRanges();
 
-  private transient int currentRangeIdx;
+  public abstract int getSize();
 
-  public SparseFileContent() {
-    ranges = new ArrayList<>();
+  public static SparseFileContent create(ImmutableList<Range> ranges, int size) {
+    return new AutoValue_SparseFileContent(ranges, size);
   }
 
-  public int size() {
-    return size;
+  @VisibleForTesting
+  public int getRangesCount() {
+    return getRanges().size();
   }
 
-  public void setSize(int s) {
-    size = s;
+  public Accessor createAccessor() {
+    return new Accessor(this);
   }
 
-  public String get(int idx) {
-    final String line = getLine(idx);
-    if (line == null) {
-      throw new ArrayIndexOutOfBoundsException(idx);
-    }
-    return line;
-  }
+  /**
+   * Provide a methods to work with the content of a {@link SparseFileContent}.
+   *
+   * <p>The class hides internal representation of a {@link SparseFileContent} and provides
+   * convenient way for accessing a content.
+   */
+  public static class Accessor {
+    private final SparseFileContent content;
+    private int currentRangeIdx;
 
-  public boolean contains(int idx) {
-    return getLine(idx) != null;
-  }
-
-  public int first() {
-    return ranges.isEmpty() ? size() : ranges.get(0).base;
-  }
-
-  public int next(int idx) {
-    // Most requests are sequential in nature, fetching the next
-    // line from the current range, or the immediate next range.
-    //
-    int high = ranges.size();
-    if (currentRangeIdx < high) {
-      Range cur = ranges.get(currentRangeIdx);
-      if (cur.contains(idx + 1)) {
-        return idx + 1;
-      }
-
-      if (++currentRangeIdx < high) {
-        // Its not plus one, its the base of the next range.
-        //
-        return ranges.get(currentRangeIdx).base;
-      }
+    private Accessor(SparseFileContent content) {
+      this.content = content;
     }
 
-    // Binary search for the current value, since we know its a sorted list.
-    //
-    int low = 0;
-    do {
-      final int mid = (low + high) / 2;
-      final Range cur = ranges.get(mid);
+    public String get(int idx) {
+      final String line = getLine(idx);
+      if (line == null) {
+        throw new ArrayIndexOutOfBoundsException(idx);
+      }
+      return line;
+    }
 
-      if (cur.contains(idx)) {
+    public int getSize() {
+      return content.getSize();
+    }
+
+    public boolean contains(int idx) {
+      return getLine(idx) != null;
+    }
+
+    public int first() {
+      return content.getRanges().isEmpty() ? getSize() : content.getRanges().get(0).getBase();
+    }
+
+    public int next(int idx) {
+      // Most requests are sequential in nature, fetching the next
+      // line from the current range, or the immediate next range.
+      //
+      ImmutableList<Range> ranges = content.getRanges();
+      int high = ranges.size();
+      if (currentRangeIdx < high) {
+        Range cur = ranges.get(currentRangeIdx);
         if (cur.contains(idx + 1)) {
-          // Trivial plus one case above failed due to wrong currentRangeIdx.
-          // Reset the cache so we don't miss in the future.
-          //
-          currentRangeIdx = mid;
           return idx + 1;
         }
 
-        if (mid + 1 < ranges.size()) {
-          // Its the base of the next range.
-          currentRangeIdx = mid + 1;
-          return ranges.get(currentRangeIdx).base;
-        }
-
-        // No more lines in the file.
-        //
-        return size();
-      }
-
-      if (idx < cur.base) {
-        high = mid;
-      } else {
-        low = mid + 1;
-      }
-    } while (low < high);
-
-    return size();
-  }
-
-  private String getLine(int idx) {
-    // Most requests are sequential in nature, fetching the next
-    // line from the current range, or the next range.
-    //
-    int high = ranges.size();
-    if (currentRangeIdx < high) {
-      Range cur = ranges.get(currentRangeIdx);
-      if (cur.contains(idx)) {
-        return cur.get(idx);
-      }
-
-      if (++currentRangeIdx < high) {
-        final Range next = ranges.get(currentRangeIdx);
-        if (next.contains(idx)) {
-          return next.get(idx);
+        if (++currentRangeIdx < high) {
+          // Its not plus one, its the base of the next range.
+          //
+          return ranges.get(currentRangeIdx).getBase();
         }
       }
+
+      // Binary search for the current value, since we know its a sorted list.
+      //
+      int low = 0;
+      do {
+        final int mid = (low + high) / 2;
+        final Range cur = ranges.get(mid);
+
+        if (cur.contains(idx)) {
+          if (cur.contains(idx + 1)) {
+            // Trivial plus one case above failed due to wrong currentRangeIdx.
+            // Reset the cache so we don't miss in the future.
+            //
+            currentRangeIdx = mid;
+            return idx + 1;
+          }
+
+          if (mid + 1 < ranges.size()) {
+            // Its the base of the next range.
+            currentRangeIdx = mid + 1;
+            return ranges.get(currentRangeIdx).getBase();
+          }
+
+          // No more lines in the file.
+          //
+          return getSize();
+        }
+
+        if (idx < cur.getBase()) {
+          high = mid;
+        } else {
+          low = mid + 1;
+        }
+      } while (low < high);
+
+      return getSize();
     }
 
-    // Binary search for the range, since we know its a sorted list.
-    //
-    if (ranges.isEmpty()) {
+    private String getLine(int idx) {
+      // Most requests are sequential in nature, fetching the next
+      // line from the current range, or the next range.
+      //
+      ImmutableList<Range> ranges = content.getRanges();
+      int high = ranges.size();
+      if (currentRangeIdx < high) {
+        Range cur = ranges.get(currentRangeIdx);
+        if (cur.contains(idx)) {
+          return cur.get(idx);
+        }
+
+        if (++currentRangeIdx < high) {
+          final Range next = ranges.get(currentRangeIdx);
+          if (next.contains(idx)) {
+            return next.get(idx);
+          }
+        }
+      }
+
+      // Binary search for the range, since we know its a sorted list.
+      //
+      if (ranges.isEmpty()) {
+        return null;
+      }
+
+      int low = 0;
+      do {
+        final int mid = (low + high) / 2;
+        final Range cur = ranges.get(mid);
+        if (cur.contains(idx)) {
+          currentRangeIdx = mid;
+          return cur.get(idx);
+        }
+        if (idx < cur.getBase()) {
+          high = mid;
+        } else {
+          low = mid + 1;
+        }
+      } while (low < high);
       return null;
     }
-
-    int low = 0;
-    do {
-      final int mid = (low + high) / 2;
-      final Range cur = ranges.get(mid);
-      if (cur.contains(idx)) {
-        currentRangeIdx = mid;
-        return cur.get(idx);
-      }
-      if (idx < cur.base) {
-        high = mid;
-      } else {
-        low = mid + 1;
-      }
-    } while (low < high);
-    return null;
-  }
-
-  public void addLine(int i, String content) {
-    final Range r;
-    if (!ranges.isEmpty() && i == last().end()) {
-      r = last();
-    } else {
-      r = new Range(i);
-      ranges.add(r);
-    }
-    r.lines.add(content);
-  }
-
-  private Range last() {
-    return ranges.get(ranges.size() - 1);
   }
 
   @Override
-  public String toString() {
+  public final String toString() {
     final StringBuilder b = new StringBuilder();
     b.append("SparseFileContent[\n");
-    for (Range r : ranges) {
+    for (Range r : getRanges()) {
       b.append("  ");
       b.append(r.toString());
       b.append('\n');
@@ -176,33 +191,32 @@
     return b.toString();
   }
 
-  static class Range {
-    protected int base;
-    protected List<String> lines;
-
-    private Range(int b) {
-      base = b;
-      lines = new ArrayList<>();
+  @AutoValue
+  abstract static class Range {
+    static Range create(int base, ImmutableList<String> lines) {
+      return new AutoValue_SparseFileContent_Range(base, lines);
     }
 
-    protected Range() {}
+    abstract int getBase();
+
+    abstract ImmutableList<String> getLines();
 
     private String get(int i) {
-      return lines.get(i - base);
+      return getLines().get(i - getBase());
     }
 
     private int end() {
-      return base + lines.size();
+      return getBase() + getLines().size();
     }
 
     private boolean contains(int i) {
-      return base <= i && i < end();
+      return getBase() <= i && i < end();
     }
 
     @Override
-    public String toString() {
+    public final String toString() {
       // Usage of [ and ) is intentional to denote inclusive/exclusive range
-      return "Range[" + base + "," + end() + ")";
+      return "Range[" + getBase() + "," + end() + ")";
     }
   }
 }
diff --git a/java/com/google/gerrit/prettify/common/SparseFileContentBuilder.java b/java/com/google/gerrit/prettify/common/SparseFileContentBuilder.java
new file mode 100644
index 0000000..04fb5d1
--- /dev/null
+++ b/java/com/google/gerrit/prettify/common/SparseFileContentBuilder.java
@@ -0,0 +1,90 @@
+// Copyright (C) 2019 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.prettify.common;
+
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.prettify.common.SparseFileContent.Range;
+
+/**
+ * A builder for creating immutable {@link SparseFileContent}. Lines can be only be added in
+ * sequential (increased) order
+ */
+public class SparseFileContentBuilder {
+  private final ImmutableList.Builder<Range> ranges;
+  private final int size;
+  private int lastRangeBase;
+  private int lastRangeEnd;
+  private ImmutableList.Builder<String> lastRangeLines;
+
+  public SparseFileContentBuilder(int size) {
+    ranges = new ImmutableList.Builder<>();
+    startNextRange(0);
+    this.size = size;
+  }
+
+  public void addLine(int lineNumber, String content) {
+    if (lineNumber < 0) {
+      throw new IllegalArgumentException("Line number must be non-negative");
+    }
+    //    if (lineNumber >= size) {
+    //     The following 4 tests are failed if you uncomment this condition:
+    //
+    //
+    // diffOfFileWithMultilineRebaseHunkRemovingNewlineAtEndOfFileAndWithCommentReturnsFileContents
+    //
+    // diffOfFileWithMultilineRebaseHunkAddingNewlineAtEndOfFileAndWithCommentReturnsFileContents
+    //
+    //
+    // diffOfFileWithMultilineRebaseHunkRemovingNewlineAtEndOfFileAndWithCommentReturnsFileContents
+    //
+    // diffOfFileWithMultilineRebaseHunkAddingNewlineAtEndOfFileAndWithCommentReturnsFileContents
+    //     Tests are failed because there are some bug with diff calculation.
+    //     The condition must be uncommented after all these bugs are fixed.
+    //     Also don't forget to remove ignore from for SparseFileContentBuilder
+    //      throw new IllegalArgumentException(String.format("The zero-based line number %d is after
+    // the end of file. The file size is %d line(s).", lineNumber, size));
+    //    }
+    if (lineNumber < lastRangeEnd) {
+      throw new IllegalArgumentException(
+          String.format(
+              "Invalid line number %d. You are trying to add a line before an already added line"
+                  + " %d",
+              lineNumber, lastRangeEnd));
+    }
+    if (lineNumber > lastRangeEnd) {
+      finishLastRange();
+      startNextRange(lineNumber);
+    }
+    lastRangeLines.add(content);
+    lastRangeEnd++;
+  }
+
+  private void startNextRange(int base) {
+    lastRangeLines = new ImmutableList.Builder<>();
+    lastRangeBase = lastRangeEnd = base;
+  }
+
+  private void finishLastRange() {
+    if (lastRangeEnd > lastRangeBase) {
+      ranges.add(Range.create(lastRangeBase, lastRangeLines.build()));
+      lastRangeLines = null;
+    }
+  }
+
+  public SparseFileContent build() {
+    finishLastRange();
+    return SparseFileContent.create(ranges.build(), size);
+  }
+}
diff --git a/java/com/google/gerrit/prettify/common/testing/BUILD b/java/com/google/gerrit/prettify/common/testing/BUILD
new file mode 100644
index 0000000..5057fdb
--- /dev/null
+++ b/java/com/google/gerrit/prettify/common/testing/BUILD
@@ -0,0 +1,14 @@
+load("@rules_java//java:defs.bzl", "java_library")
+
+package(default_testonly = True)
+
+java_library(
+    name = "testing",
+    srcs = glob(["*.java"]),
+    visibility = ["//visibility:public"],
+    deps = [
+        "//java/com/google/gerrit/prettify:server",
+        "//lib:guava",
+        "//lib/truth",
+    ],
+)
diff --git a/java/com/google/gerrit/prettify/common/testing/SparseFileContentSubject.java b/java/com/google/gerrit/prettify/common/testing/SparseFileContentSubject.java
new file mode 100644
index 0000000..c1fe1ec
--- /dev/null
+++ b/java/com/google/gerrit/prettify/common/testing/SparseFileContentSubject.java
@@ -0,0 +1,65 @@
+// Copyright (C) 2019 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.prettify.common.testing;
+
+import static com.google.common.truth.Truth.assertAbout;
+
+import com.google.common.truth.FailureMetadata;
+import com.google.common.truth.IntegerSubject;
+import com.google.common.truth.MapSubject;
+import com.google.common.truth.Subject;
+import com.google.gerrit.prettify.common.SparseFileContent;
+import java.util.HashMap;
+import java.util.Map;
+
+public class SparseFileContentSubject extends Subject {
+  public static SparseFileContentSubject assertThat(SparseFileContent sparseFileContent) {
+    return assertAbout(sparseFileContent()).that(sparseFileContent);
+  }
+
+  private final SparseFileContent sparseFileContent;
+
+  private SparseFileContentSubject(FailureMetadata metadata, SparseFileContent actual) {
+    super(metadata, actual);
+    this.sparseFileContent = actual;
+  }
+
+  private static Subject.Factory<SparseFileContentSubject, SparseFileContent> sparseFileContent() {
+    return SparseFileContentSubject::new;
+  }
+
+  public IntegerSubject getSize() {
+    isNotNull();
+    return check("size()").that(sparseFileContent.getSize());
+  }
+
+  public IntegerSubject getRangesCount() {
+    isNotNull();
+    return check("rangesCount()").that(sparseFileContent.getRangesCount());
+  }
+
+  public MapSubject lines() {
+    isNotNull();
+    Map<Integer, String> lines = new HashMap<>();
+    SparseFileContent.Accessor accessor = sparseFileContent.createAccessor();
+    int size = accessor.getSize();
+    int idx = accessor.first();
+    while (idx < size) {
+      lines.put(idx, accessor.get(idx));
+      idx = accessor.next(idx);
+    }
+    return check("lines()").that(lines);
+  }
+}
diff --git a/java/com/google/gerrit/server/ExceptionHook.java b/java/com/google/gerrit/server/ExceptionHook.java
index db44b4b..019a715 100644
--- a/java/com/google/gerrit/server/ExceptionHook.java
+++ b/java/com/google/gerrit/server/ExceptionHook.java
@@ -34,6 +34,12 @@
    * <p>Only affects operations that are executed with {@link
    * com.google.gerrit.server.update.RetryHelper}.
    *
+   * <p>Should return {@code true} only for exceptions that are caused by temporary issues where a
+   * retry of the operation has a chance to succeed.
+   *
+   * <p>If {@code false} is returned the operation is still retried once to capture a trace, unless
+   * {@link #skipRetryWithTrace(Throwable)} skips the auto-retry.
+   *
    * @param throwable throwable that was thrown while executing the operation
    * @return whether the operation should be retried
    */
@@ -42,6 +48,34 @@
   }
 
   /**
+   * Whether auto-retrying of an operation with tracing should be skipped for the given throwable.
+   *
+   * <p>Only affects operations that are executed with {@link
+   * com.google.gerrit.server.update.RetryHelper}.
+   *
+   * <p>This method is only called for exceptions for which the operation should not be retried
+   * ({@link #shouldRetry(Throwable)} returned {@code false}).
+   *
+   * <p>By default this method returns {@code false}, so that by default traces for unexpected
+   * exceptions are captured, which allows to investigate them.
+   *
+   * <p>Implementors may use this method to skip retry with tracing for exceptions that occur due to
+   * known causes that are permanent and where a trace is not needed for the investigation. For
+   * example, if an operation fails because persisted data is corrupt, it makes no sense to retry
+   * the operation with a trace, because the trace will not help with fixing the corrupt data.
+   *
+   * <p>This method is only invoked if retry with tracing is enabled on the server ({@code
+   * retry.retryWithTraceOnFailure} in {@code gerrit.config} is set to {@code true}).
+   *
+   * @param throwable throwable that was thrown while executing the operation
+   * @return whether auto-retrying of an operation with tracing should be skipped for the given
+   *     throwable
+   */
+  default boolean skipRetryWithTrace(Throwable throwable) {
+    return false;
+  }
+
+  /**
    * Formats the cause of an exception for use in metrics.
    *
    * <p>This method allows implementors to group exceptions that have the same cause into one metric
@@ -55,7 +89,9 @@
   }
 
   /**
-   * Returns an error message that should be returned to the user.
+   * Returns a message that should be returned to the user.
+   *
+   * <p>This message is included into the HTTP response that is sent to the user.
    *
    * @param throwable throwable that was thrown while executing an operation
    * @return error message that should be returned to the user, {@link Optional#empty()} if no
@@ -64,4 +100,25 @@
   default Optional<String> getUserMessage(Throwable throwable) {
     return Optional.empty();
   }
+
+  /**
+   * Returns the HTTP status code that should be returned to the user.
+   *
+   * <p>If no value is returned ({@link Optional#empty()}) the HTTP status code defaults to {@code
+   * 500 Internal Server Error}.
+   *
+   * <p>{@link #getUserMessage(Throwable)} allows to define which message should be included into
+   * the body of the HTTP response.
+   *
+   * <p>Implementors may use this method to change the status code for certain exceptions (e.g.
+   * using this method it would be possible to return {@code 409 Conflict} for {@link
+   * com.google.gerrit.git.LockFailureException}s instead of {@code 500 Internal Server Error}).
+   *
+   * @param throwable throwable that was thrown while executing an operation
+   * @return HTTP status code that should be returned to the user, {@link Optional#empty()} if the
+   *     exception should result in {@code 500 Internal Server Error}
+   */
+  default Optional<Integer> getStatusCode(Throwable throwable) {
+    return Optional.empty();
+  }
 }
diff --git a/java/com/google/gerrit/server/diff/DiffInfoCreator.java b/java/com/google/gerrit/server/diff/DiffInfoCreator.java
new file mode 100644
index 0000000..c29ffc8
--- /dev/null
+++ b/java/com/google/gerrit/server/diff/DiffInfoCreator.java
@@ -0,0 +1,299 @@
+// Copyright (C) 2019 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.diff;
+
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.common.data.PatchScript;
+import com.google.gerrit.common.data.PatchScript.DisplayMethod;
+import com.google.gerrit.common.data.PatchScript.PatchScriptFileInfo;
+import com.google.gerrit.entities.Patch;
+import com.google.gerrit.extensions.common.ChangeType;
+import com.google.gerrit.extensions.common.DiffInfo;
+import com.google.gerrit.extensions.common.DiffInfo.ContentEntry;
+import com.google.gerrit.extensions.common.DiffInfo.FileMeta;
+import com.google.gerrit.extensions.common.DiffInfo.IntraLineStatus;
+import com.google.gerrit.extensions.common.DiffWebLinkInfo;
+import com.google.gerrit.extensions.common.WebLinkInfo;
+import com.google.gerrit.jgit.diff.ReplaceEdit;
+import com.google.gerrit.prettify.common.SparseFileContent;
+import com.google.gerrit.server.change.FileContentUtil;
+import com.google.gerrit.server.project.ProjectState;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import org.eclipse.jgit.diff.Edit;
+
+/** Creates and fills a new {@link DiffInfo} object based on diff between files. */
+public class DiffInfoCreator {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  private static final ImmutableMap<Patch.ChangeType, ChangeType> CHANGE_TYPE =
+      Maps.immutableEnumMap(
+          new ImmutableMap.Builder<Patch.ChangeType, ChangeType>()
+              .put(Patch.ChangeType.ADDED, ChangeType.ADDED)
+              .put(Patch.ChangeType.MODIFIED, ChangeType.MODIFIED)
+              .put(Patch.ChangeType.DELETED, ChangeType.DELETED)
+              .put(Patch.ChangeType.RENAMED, ChangeType.RENAMED)
+              .put(Patch.ChangeType.COPIED, ChangeType.COPIED)
+              .put(Patch.ChangeType.REWRITE, ChangeType.REWRITE)
+              .build());
+
+  private final DiffWebLinksProvider webLinksProvider;
+  private final boolean intraline;
+  private final ProjectState state;
+
+  public DiffInfoCreator(
+      ProjectState state, DiffWebLinksProvider webLinksProvider, boolean intraline) {
+    this.webLinksProvider = webLinksProvider;
+    this.state = state;
+    this.intraline = intraline;
+  }
+
+  /* Returns the {@link DiffInfo} to display for end-users */
+  public DiffInfo create(PatchScript ps, DiffSide sideA, DiffSide sideB) {
+    DiffInfo result = new DiffInfo();
+
+    ImmutableList<DiffWebLinkInfo> links = webLinksProvider.getDiffLinks();
+    result.webLinks = links.isEmpty() ? null : links;
+
+    if (ps.isBinary()) {
+      result.binary = true;
+    }
+    result.metaA = createFileMeta(sideA).orElse(null);
+    result.metaB = createFileMeta(sideB).orElse(null);
+
+    if (intraline) {
+      if (ps.hasIntralineTimeout()) {
+        result.intralineStatus = IntraLineStatus.TIMEOUT;
+      } else if (ps.hasIntralineFailure()) {
+        result.intralineStatus = IntraLineStatus.FAILURE;
+      } else {
+        result.intralineStatus = IntraLineStatus.OK;
+      }
+      logger.atFine().log("intralineStatus = %s", result.intralineStatus);
+    }
+
+    result.changeType = CHANGE_TYPE.get(ps.getChangeType());
+    logger.atFine().log("changeType = %s", result.changeType);
+    if (result.changeType == null) {
+      throw new IllegalStateException("unknown change type: " + ps.getChangeType());
+    }
+
+    if (ps.getPatchHeader().size() > 0) {
+      result.diffHeader = ps.getPatchHeader();
+    }
+    result.content = calculateDiffContentEntries(ps);
+    return result;
+  }
+
+  private static List<ContentEntry> calculateDiffContentEntries(PatchScript ps) {
+    ContentCollector contentCollector = new ContentCollector(ps);
+    Set<Edit> editsDueToRebase = ps.getEditsDueToRebase();
+    for (Edit edit : ps.getEdits()) {
+      logger.atFine().log("next edit = %s", edit);
+
+      if (edit.getType() == Edit.Type.EMPTY) {
+        logger.atFine().log("skip empty edit");
+        continue;
+      }
+      contentCollector.addCommon(edit.getBeginA());
+
+      checkState(
+          contentCollector.nextA == edit.getBeginA(),
+          "nextA = %s; want %s",
+          contentCollector.nextA,
+          edit.getBeginA());
+      checkState(
+          contentCollector.nextB == edit.getBeginB(),
+          "nextB = %s; want %s",
+          contentCollector.nextB,
+          edit.getBeginB());
+      switch (edit.getType()) {
+        case DELETE:
+        case INSERT:
+        case REPLACE:
+          List<Edit> internalEdit =
+              edit instanceof ReplaceEdit ? ((ReplaceEdit) edit).getInternalEdits() : null;
+          boolean dueToRebase = editsDueToRebase.contains(edit);
+          contentCollector.addDiff(edit.getEndA(), edit.getEndB(), internalEdit, dueToRebase);
+          break;
+        case EMPTY:
+        default:
+          throw new IllegalStateException();
+      }
+    }
+    contentCollector.addCommon(ps.getA().getSize());
+
+    return contentCollector.lines;
+  }
+
+  private Optional<FileMeta> createFileMeta(DiffSide side) {
+    PatchScriptFileInfo fileInfo = side.fileInfo();
+    if (fileInfo.displayMethod == DisplayMethod.NONE) {
+      return Optional.empty();
+    }
+    FileMeta result = new FileMeta();
+    result.name = side.fileName();
+    result.contentType =
+        FileContentUtil.resolveContentType(
+            state, side.fileName(), fileInfo.mode, fileInfo.mimeType);
+    result.lines = fileInfo.content.getSize();
+    ImmutableList<WebLinkInfo> links = webLinksProvider.getFileWebLinks(side.type());
+    result.webLinks = links.isEmpty() ? null : links;
+    result.commitId = fileInfo.commitId;
+    return Optional.of(result);
+  }
+
+  private static class ContentCollector {
+
+    private final List<ContentEntry> lines;
+    private final SparseFileContent.Accessor fileA;
+    private final SparseFileContent.Accessor fileB;
+    private final boolean ignoreWS;
+
+    private int nextA;
+    private int nextB;
+
+    ContentCollector(PatchScript ps) {
+      lines = Lists.newArrayListWithExpectedSize(ps.getEdits().size() + 2);
+      fileA = ps.getA().createAccessor();
+      fileB = ps.getB().createAccessor();
+      ignoreWS = ps.isIgnoreWhitespace();
+    }
+
+    void addCommon(int end) {
+      logger.atFine().log("addCommon: end = %d", end);
+
+      end = Math.min(end, fileA.getSize());
+      logger.atFine().log("end = %d", end);
+
+      if (nextA >= end) {
+        logger.atFine().log("nextA >= end: nextA = %d, end = %d", nextA, end);
+        return;
+      }
+
+      while (nextA < end) {
+        logger.atFine().log("nextA < end: nextA = %d, end = %d", nextA, end);
+
+        if (!fileA.contains(nextA)) {
+          logger.atFine().log("fileA does not contain nextA: nextA = %d", nextA);
+
+          int endRegion = Math.min(end, nextA == 0 ? fileA.first() : fileA.next(nextA - 1));
+          int len = endRegion - nextA;
+          entry().skip = len;
+          nextA = endRegion;
+          nextB += len;
+
+          logger.atFine().log("setting: nextA = %d, nextB = %d", nextA, nextB);
+          continue;
+        }
+
+        ContentEntry e = null;
+        for (int i = nextA; i == nextA && i < end; i = fileA.next(i), nextA++, nextB++) {
+          if (ignoreWS && fileB.contains(nextB)) {
+            if (e == null || e.common == null) {
+              logger.atFine().log("create new common entry: nextA = %d, nextB = %d", nextA, nextB);
+              e = entry();
+              e.a = Lists.newArrayListWithCapacity(end - nextA);
+              e.b = Lists.newArrayListWithCapacity(end - nextA);
+              e.common = true;
+            }
+            e.a.add(fileA.get(nextA));
+            e.b.add(fileB.get(nextB));
+          } else {
+            if (e == null || e.common != null) {
+              logger.atFine().log(
+                  "create new non-common entry: nextA = %d, nextB = %d", nextA, nextB);
+              e = entry();
+              e.ab = Lists.newArrayListWithCapacity(end - nextA);
+            }
+            e.ab.add(fileA.get(nextA));
+          }
+        }
+      }
+    }
+
+    void addDiff(int endA, int endB, List<Edit> internalEdit, boolean dueToRebase) {
+      logger.atFine().log(
+          "addDiff: endA = %d, endB = %d, numberOfInternalEdits = %d, dueToRebase = %s",
+          endA, endB, internalEdit != null ? internalEdit.size() : 0, dueToRebase);
+
+      int lenA = endA - nextA;
+      int lenB = endB - nextB;
+      logger.atFine().log("lenA = %d, lenB = %d", lenA, lenB);
+      checkState(lenA > 0 || lenB > 0);
+
+      logger.atFine().log("create non-common entry");
+      ContentEntry e = entry();
+      if (lenA > 0) {
+        logger.atFine().log("lenA > 0: lenA = %d", lenA);
+        e.a = Lists.newArrayListWithCapacity(lenA);
+        for (; nextA < endA; nextA++) {
+          e.a.add(fileA.get(nextA));
+        }
+      }
+      if (lenB > 0) {
+        logger.atFine().log("lenB > 0: lenB = %d", lenB);
+        e.b = Lists.newArrayListWithCapacity(lenB);
+        for (; nextB < endB; nextB++) {
+          e.b.add(fileB.get(nextB));
+        }
+      }
+      if (internalEdit != null && !internalEdit.isEmpty()) {
+        logger.atFine().log("processing internal edits");
+
+        e.editA = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
+        e.editB = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
+        int lastA = 0;
+        int lastB = 0;
+        for (Edit edit : internalEdit) {
+          logger.atFine().log("internal edit = %s", edit);
+
+          if (edit.getBeginA() != edit.getEndA()) {
+            logger.atFine().log(
+                "edit.getBeginA() != edit.getEndA(): edit.getBeginA() = %d, edit.getEndA() = %d",
+                edit.getBeginA(), edit.getEndA());
+            e.editA.add(
+                ImmutableList.of(edit.getBeginA() - lastA, edit.getEndA() - edit.getBeginA()));
+            lastA = edit.getEndA();
+            logger.atFine().log("lastA = %d", lastA);
+          }
+          if (edit.getBeginB() != edit.getEndB()) {
+            logger.atFine().log(
+                "edit.getBeginB() != edit.getEndB(): edit.getBeginB() = %d, edit.getEndB() = %d",
+                edit.getBeginB(), edit.getEndB());
+            e.editB.add(
+                ImmutableList.of(edit.getBeginB() - lastB, edit.getEndB() - edit.getBeginB()));
+            lastB = edit.getEndB();
+            logger.atFine().log("lastB = %d", lastB);
+          }
+        }
+      }
+      e.dueToRebase = dueToRebase ? true : null;
+    }
+
+    private ContentEntry entry() {
+      ContentEntry e = new ContentEntry();
+      lines.add(e);
+      return e;
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/diff/DiffSide.java b/java/com/google/gerrit/server/diff/DiffSide.java
new file mode 100644
index 0000000..28c7810
--- /dev/null
+++ b/java/com/google/gerrit/server/diff/DiffSide.java
@@ -0,0 +1,37 @@
+// Copyright (C) 2019 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.diff;
+
+import com.google.auto.value.AutoValue;
+import com.google.gerrit.common.data.PatchScript.PatchScriptFileInfo;
+
+/** Contains settings for one of two sides in diff view. Each diff view has exactly 2 sides. */
+@AutoValue
+public abstract class DiffSide {
+  public enum Type {
+    SIDE_A,
+    SIDE_B
+  }
+
+  public static DiffSide create(PatchScriptFileInfo fileInfo, String fileName, Type type) {
+    return new AutoValue_DiffSide(fileInfo, fileName, type);
+  }
+
+  public abstract PatchScriptFileInfo fileInfo();
+
+  public abstract String fileName();
+
+  public abstract Type type();
+}
diff --git a/java/com/google/gerrit/server/diff/DiffWebLinksProvider.java b/java/com/google/gerrit/server/diff/DiffWebLinksProvider.java
new file mode 100644
index 0000000..0f71b17
--- /dev/null
+++ b/java/com/google/gerrit/server/diff/DiffWebLinksProvider.java
@@ -0,0 +1,29 @@
+// Copyright (C) 2019 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.diff;
+
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.extensions.common.DiffWebLinkInfo;
+import com.google.gerrit.extensions.common.WebLinkInfo;
+
+/** Provider for different types of links which can be displayed in a diff view. */
+public interface DiffWebLinksProvider {
+
+  /** Returns links associated with the diff view */
+  ImmutableList<DiffWebLinkInfo> getDiffLinks();
+
+  /** Returns links associated with the diff side */
+  ImmutableList<WebLinkInfo> getFileWebLinks(DiffSide.Type fileInfoType);
+}
diff --git a/java/com/google/gerrit/server/git/MergeUtil.java b/java/com/google/gerrit/server/git/MergeUtil.java
index 8475d03..4495317 100644
--- a/java/com/google/gerrit/server/git/MergeUtil.java
+++ b/java/com/google/gerrit/server/git/MergeUtil.java
@@ -40,6 +40,7 @@
 import com.google.gerrit.entities.LabelId;
 import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
+import com.google.gerrit.exceptions.InvalidMergeStrategyException;
 import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.extensions.registration.DynamicSet;
@@ -265,7 +266,8 @@
       boolean ignoreIdenticalTree,
       boolean allowConflicts)
       throws MissingObjectException, IncorrectObjectTypeException, IOException,
-          MergeIdenticalTreeException, MergeConflictException, MethodNotAllowedException {
+          MergeIdenticalTreeException, MergeConflictException, MethodNotAllowedException,
+          InvalidMergeStrategyException {
 
     ThreeWayMerger m = newThreeWayMerger(inserter, repoConfig);
     m.setBase(originalCommit.getParent(parentIndex));
@@ -431,7 +433,8 @@
       PersonIdent committerIndent,
       String commitMsg,
       RevWalk rw)
-      throws IOException, MergeIdenticalTreeException, MergeConflictException {
+      throws IOException, MergeIdenticalTreeException, MergeConflictException,
+          InvalidMergeStrategyException {
 
     if (!MergeStrategy.THEIRS.getName().equals(mergeStrategy)
         && rw.isMergedInto(originalCommit, mergeTip)) {
@@ -745,7 +748,7 @@
       BranchNameKey destBranch,
       CodeReviewCommit mergeTip,
       CodeReviewCommit n)
-      throws IntegrationException {
+      throws IntegrationException, InvalidMergeStrategyException {
     ThreeWayMerger m = newThreeWayMerger(inserter, repoConfig);
     try {
       if (m.merge(mergeTip, n)) {
@@ -866,7 +869,8 @@
         .collect(joining(",", "Merge changes ", merged.size() > 5 ? ", ..." : ""));
   }
 
-  public ThreeWayMerger newThreeWayMerger(ObjectInserter inserter, Config repoConfig) {
+  public ThreeWayMerger newThreeWayMerger(ObjectInserter inserter, Config repoConfig)
+      throws InvalidMergeStrategyException {
     return newThreeWayMerger(inserter, repoConfig, mergeStrategyName());
   }
 
@@ -890,7 +894,8 @@
   }
 
   public static ThreeWayMerger newThreeWayMerger(
-      ObjectInserter inserter, Config repoConfig, String strategyName) {
+      ObjectInserter inserter, Config repoConfig, String strategyName)
+      throws InvalidMergeStrategyException {
     Merger m = newMerger(inserter, repoConfig, strategyName);
     checkArgument(
         m instanceof ThreeWayMerger,
@@ -899,9 +904,12 @@
     return (ThreeWayMerger) m;
   }
 
-  public static Merger newMerger(ObjectInserter inserter, Config repoConfig, String strategyName) {
+  public static Merger newMerger(ObjectInserter inserter, Config repoConfig, String strategyName)
+      throws InvalidMergeStrategyException {
     MergeStrategy strategy = MergeStrategy.get(strategyName);
-    checkArgument(strategy != null, "invalid merge strategy: %s", strategyName);
+    if (strategy == null) {
+      throw new InvalidMergeStrategyException(strategyName);
+    }
     return strategy.newMerger(
         new ObjectInserter.Filter() {
           @Override
diff --git a/java/com/google/gerrit/server/git/PermissionAwareReadOnlyRefDatabase.java b/java/com/google/gerrit/server/git/PermissionAwareReadOnlyRefDatabase.java
index f7472b9..060000a 100644
--- a/java/com/google/gerrit/server/git/PermissionAwareReadOnlyRefDatabase.java
+++ b/java/com/google/gerrit/server/git/PermissionAwareReadOnlyRefDatabase.java
@@ -32,6 +32,8 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.lib.ObjectId;
@@ -105,11 +107,25 @@
 
     Collection<Ref> result;
     try {
+      // The security filtering assumes to receive the same refMap, independently from the ref
+      // prefix offset
       result = forProject.filter(refs.values(), getDelegate(), RefFilterOptions.defaults());
     } catch (PermissionBackendException e) {
       throw new IOException("");
     }
-    return result.stream().collect(toMap(Ref::getName, r -> r));
+    return buildPrefixRefMap(prefix, result);
+  }
+
+  private Map<String, Ref> buildPrefixRefMap(String prefix, Collection<Ref> refs) {
+    int prefixSlashPos = prefix.lastIndexOf('/') + 1;
+    if (prefixSlashPos > 0) {
+      return refs.stream()
+          .collect(
+              Collectors.toMap(
+                  (Ref ref) -> ref.getName().substring(prefixSlashPos), Function.identity()));
+    }
+
+    return refs.stream().collect(toMap(Ref::getName, r -> r));
   }
 
   @Override
diff --git a/java/com/google/gerrit/server/patch/PatchScriptBuilder.java b/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
index 1435c5e..0a17303 100644
--- a/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
+++ b/java/com/google/gerrit/server/patch/PatchScriptBuilder.java
@@ -17,6 +17,7 @@
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Comparator.comparing;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.gerrit.common.data.CommentDetail;
 import com.google.gerrit.common.data.PatchScript;
@@ -24,11 +25,11 @@
 import com.google.gerrit.entities.Change;
 import com.google.gerrit.entities.Comment;
 import com.google.gerrit.entities.Patch;
-import com.google.gerrit.entities.Project;
+import com.google.gerrit.entities.Patch.ChangeType;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
 import com.google.gerrit.prettify.common.EditList;
-import com.google.gerrit.prettify.common.SparseFileContent;
+import com.google.gerrit.prettify.common.SparseFileContentBuilder;
 import com.google.gerrit.server.mime.FileTypeRegistry;
 import com.google.inject.Inject;
 import eu.medsea.mimeutil.MimeType;
@@ -39,10 +40,8 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
 import org.eclipse.jgit.diff.Edit;
-import org.eclipse.jgit.errors.CorruptObjectException;
-import org.eclipse.jgit.errors.IncorrectObjectTypeException;
-import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.lib.ObjectId;
@@ -59,28 +58,17 @@
 
   private static final Comparator<Edit> EDIT_SORT = comparing(Edit::getBeginA);
 
-  private Repository db;
-  private Project.NameKey projectKey;
-  private ObjectReader reader;
   private Change change;
   private DiffPreferencesInfo diffPrefs;
-  private ComparisonType comparisonType;
-  private ObjectId aId;
-  private ObjectId bId;
   private List<Edit> edits;
   private final FileTypeRegistry registry;
-  private final PatchListCache patchListCache;
   private int context;
+  private IntraLineDiffCalculator intralineDiffCalculator;
+  private SidesResolver sidesResolver;
 
   @Inject
-  PatchScriptBuilder(FileTypeRegistry ftr, PatchListCache plc) {
+  PatchScriptBuilder(FileTypeRegistry ftr) {
     registry = ftr;
-    patchListCache = plc;
-  }
-
-  void setRepository(Repository r, Project.NameKey projectKey) {
-    this.db = r;
-    this.projectKey = projectKey;
   }
 
   void setChange(Change c) {
@@ -98,62 +86,39 @@
     }
   }
 
-  void setTrees(ComparisonType ct, ObjectId a, ObjectId b) {
-    comparisonType = ct;
-    aId = a;
-    bId = b;
+  void setIntraLineDiffCalculator(IntraLineDiffCalculator calculator) {
+    intralineDiffCalculator = calculator;
   }
 
-  PatchScript toPatchScript(PatchListEntry content, CommentDetail comments, List<Patch> history)
-      throws IOException {
-    reader = db.newObjectReader();
-    try {
-      return build(content, comments, history);
-    } finally {
-      reader.close();
-    }
+  void setSidesResolver(SidesResolver resolver) {
+    sidesResolver = resolver;
   }
 
-  private PatchScript build(PatchListEntry content, CommentDetail comments, List<Patch> history)
+  PatchScript toPatchScript(PatchFileChange content, CommentDetail comments, List<Patch> history)
       throws IOException {
-    boolean intralineFailure = false;
-    boolean intralineTimeout = false;
+    return build(content, comments, history);
+  }
 
-    SideResolver resolver = new SideResolver();
-    Side a = resolver.resolve(oldName(content), null, aId);
-    Side b = resolver.resolve(newName(content), a, bId);
+  private PatchScript build(PatchFileChange content, CommentDetail comments, List<Patch> history)
+      throws IOException {
 
-    edits = new ArrayList<>(content.getEdits());
+    ResolvedSides sides = sidesResolver.resolveSides(registry, oldName(content), newName(content));
+    PatchSide a = sides.a;
+    PatchSide b = sides.b;
+
+    ImmutableList<Edit> contentEdits = content.getEdits();
     ImmutableSet<Edit> editsDueToRebase = content.getEditsDueToRebase();
 
-    if (isModify(content) && diffPrefs.intralineDifference && isIntralineModeAllowed(b)) {
-      IntraLineDiff d =
-          patchListCache.getIntraLineDiff(
-              IntraLineDiffKey.create(a.id, b.id, diffPrefs.ignoreWhitespace),
-              IntraLineDiffArgs.create(
-                  a.src, b.src, edits, editsDueToRebase, projectKey, bId, b.path));
-      if (d != null) {
-        switch (d.getStatus()) {
-          case EDIT_LIST:
-            edits = new ArrayList<>(d.getEdits());
-            break;
+    IntraLineDiffCalculatorResult intralineResult = IntraLineDiffCalculatorResult.NO_RESULT;
 
-          case DISABLED:
-            break;
-
-          case ERROR:
-            intralineFailure = true;
-            break;
-
-          case TIMEOUT:
-            intralineTimeout = true;
-            break;
-        }
-      } else {
-        intralineFailure = true;
-      }
+    if (isModify(content) && intralineDiffCalculator != null && isIntralineModeAllowed(b)) {
+      intralineResult =
+          intralineDiffCalculator.calculateIntraLineDiff(
+              contentEdits, editsDueToRebase, a.id, b.id, a.src, b.src, b.treeId, b.path);
     }
 
+    edits = new ArrayList<>(intralineResult.edits.orElse(contentEdits));
+
     correctForDifferencesInNewlineAtEnd(a, b);
 
     if (comments != null) {
@@ -198,8 +163,8 @@
         b.fileMode,
         content.getHeaderLines(),
         diffPrefs,
-        a.dst,
-        b.dst,
+        a.dst.build(),
+        b.dst.build(),
         edits,
         editsDueToRebase,
         a.displayMethod,
@@ -209,14 +174,14 @@
         comments,
         history,
         hugeFile,
-        intralineFailure,
-        intralineTimeout,
+        intralineResult.failure,
+        intralineResult.timeout,
         content.getPatchType() == Patch.PatchType.BINARY,
-        aId == null ? null : aId.getName(),
-        bId == null ? null : bId.getName());
+        a.treeId == null ? null : a.treeId.getName(),
+        b.treeId == null ? null : b.treeId.getName());
   }
 
-  private static boolean isModify(PatchListEntry content) {
+  private static boolean isModify(PatchFileChange content) {
     switch (content.getChangeType()) {
       case MODIFIED:
       case COPIED:
@@ -231,7 +196,7 @@
     }
   }
 
-  private static String oldName(PatchListEntry entry) {
+  private static String oldName(PatchFileChange entry) {
     switch (entry.getChangeType()) {
       case ADDED:
         return null;
@@ -246,7 +211,7 @@
     }
   }
 
-  private static String newName(PatchListEntry entry) {
+  private static String newName(PatchFileChange entry) {
     switch (entry.getChangeType()) {
       case DELETED:
         return null;
@@ -260,7 +225,7 @@
     }
   }
 
-  private static boolean isIntralineModeAllowed(Side side) {
+  private static boolean isIntralineModeAllowed(PatchSide side) {
     // The intraline diff cache keys are the same for these cases. It's better to not show
     // intraline results than showing completely wrong diffs or to run into a server error.
     return !Patch.isMagic(side.path) && !isSubmoduleCommit(side.mode);
@@ -270,7 +235,7 @@
     return mode.getObjectType() == Constants.OBJ_COMMIT;
   }
 
-  private void correctForDifferencesInNewlineAtEnd(Side a, Side b) {
+  private void correctForDifferencesInNewlineAtEnd(PatchSide a, PatchSide b) {
     // a.src.size() is the size ignoring a newline at the end whereas a.size() considers it.
     int aSize = a.src.size();
     int bSize = b.src.size();
@@ -312,11 +277,11 @@
     return list.isEmpty() ? Optional.empty() : Optional.ofNullable(list.get(list.size() - 1));
   }
 
-  private boolean isNewlineAtEndDeleted(Side a, Side b) {
+  private boolean isNewlineAtEndDeleted(PatchSide a, PatchSide b) {
     return !a.src.isMissingNewlineAtEnd() && b.src.isMissingNewlineAtEnd();
   }
 
-  private boolean isNewlineAtEndAdded(Side a, Side b) {
+  private boolean isNewlineAtEndAdded(PatchSide a, PatchSide b) {
     return a.src.isMissingNewlineAtEnd() && !b.src.isMissingNewlineAtEnd();
   }
 
@@ -434,7 +399,7 @@
     return last.getEndA() + (b - last.getEndB());
   }
 
-  private void packContent(Side a, Side b, boolean ignoredWhitespace) {
+  private void packContent(PatchSide a, PatchSide b, boolean ignoredWhitespace) {
     EditList list = new EditList(edits, context, a.size(), b.size());
     for (EditList.Hunk hunk : list.getHunks()) {
       while (hunk.next()) {
@@ -468,8 +433,8 @@
     }
   }
 
-  private static class Side {
-
+  private static class PatchSide {
+    final ObjectId treeId;
     final String path;
     final ObjectId id;
     final FileMode mode;
@@ -478,9 +443,10 @@
     final MimeType mimeType;
     final DisplayMethod displayMethod;
     final PatchScript.FileMode fileMode;
-    final SparseFileContent dst;
+    final SparseFileContentBuilder dst;
 
-    public Side(
+    private PatchSide(
+        ObjectId treeId,
         String path,
         ObjectId id,
         FileMode mode,
@@ -489,6 +455,7 @@
         MimeType mimeType,
         DisplayMethod displayMethod,
         PatchScript.FileMode fileMode) {
+      this.treeId = treeId;
       this.path = path;
       this.id = id;
       this.mode = mode;
@@ -497,8 +464,7 @@
       this.mimeType = mimeType;
       this.displayMethod = displayMethod;
       this.fileMode = fileMode;
-      dst = new SparseFileContent();
-      dst.setSize(size());
+      dst = new SparseFileContentBuilder(size());
     }
 
     int size() {
@@ -521,15 +487,64 @@
     }
   }
 
-  private class SideResolver {
+  interface SidesResolver {
 
-    Side resolve(final String path, final Side other, final ObjectId within) throws IOException {
+    ResolvedSides resolveSides(FileTypeRegistry typeRegistry, String oldName, String newName)
+        throws IOException;
+  }
+
+  private static class ResolvedSides {
+    // Not an @AutoValue because PatchSide can't be AutoValue
+    public final PatchSide a;
+    public final PatchSide b;
+
+    ResolvedSides(PatchSide a, PatchSide b) {
+      this.a = a;
+      this.b = b;
+    }
+  }
+
+  static class SidesResolverImpl implements SidesResolver {
+
+    private final Repository db;
+    private ComparisonType comparisonType;
+    private ObjectId aId;
+    private ObjectId bId;
+
+    SidesResolverImpl(Repository db) {
+      this.db = db;
+    }
+
+    void setTrees(ComparisonType comparisonType, ObjectId a, ObjectId b) {
+      this.comparisonType = comparisonType;
+      this.aId = a;
+      this.bId = b;
+    }
+
+    @Override
+    public ResolvedSides resolveSides(FileTypeRegistry typeRegistry, String oldName, String newName)
+        throws IOException {
+      try (ObjectReader reader = db.newObjectReader()) {
+        PatchSide a = resolve(typeRegistry, reader, oldName, null, aId);
+        PatchSide b = resolve(typeRegistry, reader, newName, a, bId);
+        return new ResolvedSides(a, b);
+      }
+    }
+
+    PatchSide resolve(
+        final FileTypeRegistry registry,
+        final ObjectReader reader,
+        final String path,
+        final PatchSide other,
+        final ObjectId within)
+        throws IOException {
       try {
         boolean isCommitMsg = Patch.COMMIT_MSG.equals(path);
         boolean isMergeList = Patch.MERGE_LIST.equals(path);
         if (isCommitMsg || isMergeList) {
           if (comparisonType.isAgainstParentOrAutoMerge() && Objects.equals(aId, within)) {
             return createSide(
+                within,
                 path,
                 ObjectId.zeroId(),
                 FileMode.MISSING,
@@ -554,6 +569,7 @@
             displayMethod = DisplayMethod.DIFF;
           }
           return createSide(
+              within,
               path,
               within,
               mode,
@@ -563,7 +579,7 @@
               displayMethod,
               false);
         }
-        final TreeWalk tw = find(path, within);
+        final TreeWalk tw = find(reader, path, within);
         ObjectId id = tw != null ? tw.getObjectId(0) : ObjectId.zeroId();
         FileMode mode = tw != null ? tw.getFileMode(0) : FileMode.MISSING;
         boolean reuse =
@@ -598,13 +614,15 @@
             displayMethod = DisplayMethod.IMG;
           }
         }
-        return createSide(path, id, mode, srcContent, src, mimeType, displayMethod, reuse);
+        return createSide(within, path, id, mode, srcContent, src, mimeType, displayMethod, reuse);
+
       } catch (IOException err) {
         throw new IOException("Cannot read " + within.name() + ":" + path, err);
       }
     }
 
-    private Side createSide(
+    private PatchSide createSide(
+        ObjectId treeId,
         String path,
         ObjectId id,
         FileMode mode,
@@ -629,12 +647,11 @@
       } else if (mode == FileMode.GITLINK) {
         fileMode = PatchScript.FileMode.GITLINK;
       }
-      return new Side(path, id, mode, srcContent, src, mimeType, displayMethod, fileMode);
+      return new PatchSide(
+          treeId, path, id, mode, srcContent, src, mimeType, displayMethod, fileMode);
     }
 
-    private TreeWalk find(String path, ObjectId within)
-        throws MissingObjectException, IncorrectObjectTypeException, CorruptObjectException,
-            IOException {
+    private TreeWalk find(ObjectReader reader, String path, ObjectId within) throws IOException {
       if (path == null || within == null) {
         return null;
       }
@@ -649,4 +666,59 @@
     return (a.getBits() & FileMode.TYPE_FILE) == FileMode.TYPE_FILE
         && (b.getBits() & FileMode.TYPE_FILE) == FileMode.TYPE_FILE;
   }
+
+  static class IntraLineDiffCalculatorResult {
+    // Not an @AutoValue because Edit is mutable
+    final boolean failure;
+    final boolean timeout;
+    private final Optional<ImmutableList<Edit>> edits;
+
+    private IntraLineDiffCalculatorResult(
+        Optional<ImmutableList<Edit>> edits, boolean failure, boolean timeout) {
+      this.failure = failure;
+      this.timeout = timeout;
+      this.edits = edits;
+    }
+
+    static final IntraLineDiffCalculatorResult NO_RESULT =
+        new IntraLineDiffCalculatorResult(Optional.empty(), false, false);
+    static final IntraLineDiffCalculatorResult FAILURE =
+        new IntraLineDiffCalculatorResult(Optional.empty(), true, false);
+    static final IntraLineDiffCalculatorResult TIMEOUT =
+        new IntraLineDiffCalculatorResult(Optional.empty(), false, true);
+
+    static IntraLineDiffCalculatorResult success(ImmutableList<Edit> edits) {
+      return new IntraLineDiffCalculatorResult(Optional.of(edits), false, false);
+    }
+  }
+
+  interface IntraLineDiffCalculator {
+
+    IntraLineDiffCalculatorResult calculateIntraLineDiff(
+        ImmutableList<Edit> edits,
+        Set<Edit> editsDueToRebase,
+        ObjectId aId,
+        ObjectId bId,
+        Text aSrc,
+        Text bSrc,
+        ObjectId bTreeId,
+        String bPath);
+  }
+
+  interface PatchFileChange {
+
+    ImmutableList<Edit> getEdits();
+
+    ImmutableSet<Edit> getEditsDueToRebase();
+
+    List<String> getHeaderLines();
+
+    String getNewName();
+
+    String getOldName();
+
+    ChangeType getChangeType();
+
+    Patch.PatchType getPatchType();
+  }
 }
diff --git a/java/com/google/gerrit/server/patch/PatchScriptFactory.java b/java/com/google/gerrit/server/patch/PatchScriptFactory.java
index ffeda3d..2c8de1d 100644
--- a/java/com/google/gerrit/server/patch/PatchScriptFactory.java
+++ b/java/com/google/gerrit/server/patch/PatchScriptFactory.java
@@ -17,6 +17,8 @@
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
 
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.data.CommentDetail;
@@ -27,6 +29,7 @@
 import com.google.gerrit.entities.Patch;
 import com.google.gerrit.entities.Patch.ChangeType;
 import com.google.gerrit.entities.PatchSet;
+import com.google.gerrit.entities.Project;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
 import com.google.gerrit.extensions.restapi.AuthException;
@@ -38,6 +41,10 @@
 import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.git.LargeObjectException;
 import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.patch.PatchScriptBuilder.IntraLineDiffCalculator;
+import com.google.gerrit.server.patch.PatchScriptBuilder.IntraLineDiffCalculatorResult;
+import com.google.gerrit.server.patch.PatchScriptBuilder.PatchFileChange;
+import com.google.gerrit.server.patch.PatchScriptBuilder.SidesResolverImpl;
 import com.google.gerrit.server.permissions.ChangePermission;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
@@ -53,15 +60,19 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.Callable;
+import org.eclipse.jgit.diff.Edit;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
 
 public class PatchScriptFactory implements Callable<PatchScript> {
+
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
   public interface Factory {
+
     PatchScriptFactory create(
         ChangeNotes notes,
         String fileName,
@@ -225,7 +236,7 @@
 
         loadCommentsAndHistory(content.getChangeType(), content.getOldName(), content.getNewName());
 
-        return b.toPatchScript(content, comments, history);
+        return b.toPatchScript(new PatchListFileChange(content), comments, history);
       } catch (PatchListNotAvailableException e) {
         throw new NoSuchChangeException(changeId, e);
       } catch (IOException e) {
@@ -256,10 +267,15 @@
 
   private PatchScriptBuilder newBuilder(PatchList list, Repository git) {
     final PatchScriptBuilder b = builderFactory.get();
-    b.setRepository(git, notes.getProjectName());
     b.setChange(notes.getChange());
     b.setDiffPrefs(diffPrefs);
-    b.setTrees(list.getComparisonType(), list.getOldId(), list.getNewId());
+    if (diffPrefs.intralineDifference) {
+      b.setIntraLineDiffCalculator(
+          new IntraLineDiffCalculatorImpl(patchListCache, notes.getProjectName(), diffPrefs));
+    }
+    SidesResolverImpl sidesResolver = new SidesResolverImpl(git);
+    sidesResolver.setTrees(list.getComparisonType(), list.getOldId(), list.getNewId());
+    b.setSidesResolver(sidesResolver);
     return b;
   }
 
@@ -402,4 +418,98 @@
       }
     }
   }
+
+  private static class IntraLineDiffCalculatorImpl implements IntraLineDiffCalculator {
+
+    private final PatchListCache patchListCache;
+    private final Project.NameKey projectKey;
+    private final DiffPreferencesInfo diffPrefs;
+
+    public IntraLineDiffCalculatorImpl(
+        PatchListCache patchListCache, Project.NameKey projectKey, DiffPreferencesInfo diffPrefs) {
+      this.patchListCache = patchListCache;
+      this.projectKey = projectKey;
+      this.diffPrefs = diffPrefs;
+    }
+
+    @Override
+    public IntraLineDiffCalculatorResult calculateIntraLineDiff(
+        ImmutableList<Edit> edits,
+        Set<Edit> editsDueToRebase,
+        ObjectId aId,
+        ObjectId bId,
+        Text aSrc,
+        Text bSrc,
+        ObjectId bTreeId,
+        String bPath) {
+      IntraLineDiff d =
+          patchListCache.getIntraLineDiff(
+              IntraLineDiffKey.create(aId, bId, diffPrefs.ignoreWhitespace),
+              IntraLineDiffArgs.create(
+                  aSrc, bSrc, edits, editsDueToRebase, projectKey, bTreeId, bPath));
+      if (d == null) {
+        return IntraLineDiffCalculatorResult.FAILURE;
+      }
+      switch (d.getStatus()) {
+        case EDIT_LIST:
+          return IntraLineDiffCalculatorResult.success(d.getEdits());
+
+        case DISABLED:
+          return IntraLineDiffCalculatorResult.NO_RESULT;
+
+        case ERROR:
+          return IntraLineDiffCalculatorResult.FAILURE;
+
+        case TIMEOUT:
+          return IntraLineDiffCalculatorResult.TIMEOUT;
+
+        default:
+          return IntraLineDiffCalculatorResult.NO_RESULT;
+      }
+    }
+  }
+
+  private static class PatchListFileChange implements PatchFileChange {
+
+    private final PatchListEntry patchListEntry;
+
+    PatchListFileChange(PatchListEntry patchListEntry) {
+      this.patchListEntry = patchListEntry;
+    }
+
+    @Override
+    public ImmutableList<Edit> getEdits() {
+      return patchListEntry.getEdits();
+    }
+
+    @Override
+    public ImmutableSet<Edit> getEditsDueToRebase() {
+      return patchListEntry.getEditsDueToRebase();
+    }
+
+    @Override
+    public String getNewName() {
+      return patchListEntry.getNewName();
+    }
+
+    @Override
+    public String getOldName() {
+      return patchListEntry.getOldName();
+    }
+
+    @Override
+    public ChangeType getChangeType() {
+      return patchListEntry.getChangeType();
+    }
+
+    @Override
+    public List<String> getHeaderLines() {
+      return patchListEntry.getHeaderLines();
+    }
+
+    @Override
+    public Patch.PatchType getPatchType() {
+      return patchListEntry.getPatchType();
+    }
+  }
 }
diff --git a/java/com/google/gerrit/server/project/RefUtil.java b/java/com/google/gerrit/server/project/RefUtil.java
index 1dac751..5d6379a 100644
--- a/java/com/google/gerrit/server/project/RefUtil.java
+++ b/java/com/google/gerrit/server/project/RefUtil.java
@@ -19,6 +19,7 @@
 
 import com.google.common.collect.Iterables;
 import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.common.Nullable;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.restapi.BadRequestException;
@@ -46,16 +47,15 @@
     try {
       ObjectId revid = repo.resolve(baseRevision);
       if (revid == null) {
-        throw new InvalidRevisionException();
+        throw new InvalidRevisionException(baseRevision);
       }
       return revid;
     } catch (IOException err) {
       logger.atSevere().withCause(err).log(
           "Cannot resolve \"%s\" in project \"%s\"", baseRevision, projectName.get());
-      throw new InvalidRevisionException();
+      throw new InvalidRevisionException(baseRevision);
     } catch (RevisionSyntaxException err) {
-      logger.atSevere().withCause(err).log("Invalid revision syntax \"%s\"", baseRevision);
-      throw new InvalidRevisionException();
+      throw new InvalidRevisionException(baseRevision);
     }
   }
 
@@ -66,7 +66,7 @@
       try {
         rw.markStart(rw.parseCommit(revid));
       } catch (IncorrectObjectTypeException err) {
-        throw new InvalidRevisionException();
+        throw new InvalidRevisionException(revid.name());
       }
       RefDatabase refDb = repo.getRefDatabase();
       Iterable<Ref> refs =
@@ -86,11 +86,11 @@
       rw.checkConnectivity();
       return rw;
     } catch (IncorrectObjectTypeException | MissingObjectException err) {
-      throw new InvalidRevisionException();
+      throw new InvalidRevisionException(revid.name());
     } catch (IOException err) {
       logger.atSevere().withCause(err).log(
           "Repository \"%s\" may be corrupt; suggest running git fsck", repo.getDirectory());
-      throw new InvalidRevisionException();
+      throw new InvalidRevisionException(revid.name());
     }
   }
 
@@ -125,8 +125,8 @@
 
     public static final String MESSAGE = "Invalid Revision";
 
-    InvalidRevisionException() {
-      super(MESSAGE);
+    InvalidRevisionException(@Nullable String invalidRevision) {
+      super(MESSAGE + ": " + invalidRevision);
     }
   }
 }
diff --git a/java/com/google/gerrit/server/restapi/change/CreateChange.java b/java/com/google/gerrit/server/restapi/change/CreateChange.java
index f4a8b75..310f71b 100644
--- a/java/com/google/gerrit/server/restapi/change/CreateChange.java
+++ b/java/com/google/gerrit/server/restapi/change/CreateChange.java
@@ -27,6 +27,7 @@
 import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
+import com.google.gerrit.exceptions.InvalidMergeStrategyException;
 import com.google.gerrit.extensions.api.changes.NotifyHandling;
 import com.google.gerrit.extensions.client.ChangeStatus;
 import com.google.gerrit.extensions.client.SubmitType;
@@ -339,8 +340,8 @@
         bu.execute();
       }
       return ins.getChange();
-    } catch (IllegalArgumentException e) {
-      throw new BadRequestException(e.getMessage(), e);
+    } catch (InvalidMergeStrategyException e) {
+      throw new BadRequestException(e.getMessage());
     }
   }
 
diff --git a/java/com/google/gerrit/server/restapi/change/GetDiff.java b/java/com/google/gerrit/server/restapi/change/GetDiff.java
index a6536ce..82bdc34 100644
--- a/java/com/google/gerrit/server/restapi/change/GetDiff.java
+++ b/java/com/google/gerrit/server/restapi/change/GetDiff.java
@@ -14,27 +14,18 @@
 
 package com.google.gerrit.server.restapi.change;
 
-import static com.google.common.base.Preconditions.checkState;
 import static com.google.gerrit.util.cli.Localizable.localizable;
 
 import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.Lists;
-import com.google.common.collect.Maps;
 import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.data.PatchScript;
-import com.google.gerrit.common.data.PatchScript.DisplayMethod;
-import com.google.gerrit.entities.Patch;
 import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo;
 import com.google.gerrit.extensions.client.DiffPreferencesInfo.Whitespace;
-import com.google.gerrit.extensions.common.ChangeType;
 import com.google.gerrit.extensions.common.DiffInfo;
-import com.google.gerrit.extensions.common.DiffInfo.ContentEntry;
-import com.google.gerrit.extensions.common.DiffInfo.FileMeta;
-import com.google.gerrit.extensions.common.DiffInfo.IntraLineStatus;
 import com.google.gerrit.extensions.common.DiffWebLinkInfo;
 import com.google.gerrit.extensions.common.WebLinkInfo;
 import com.google.gerrit.extensions.restapi.AuthException;
@@ -44,12 +35,12 @@
 import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
 import com.google.gerrit.extensions.restapi.Response;
 import com.google.gerrit.extensions.restapi.RestReadView;
-import com.google.gerrit.jgit.diff.ReplaceEdit;
-import com.google.gerrit.prettify.common.SparseFileContent;
 import com.google.gerrit.server.WebLinks;
-import com.google.gerrit.server.change.FileContentUtil;
 import com.google.gerrit.server.change.FileResource;
 import com.google.gerrit.server.change.RevisionResource;
+import com.google.gerrit.server.diff.DiffInfoCreator;
+import com.google.gerrit.server.diff.DiffSide;
+import com.google.gerrit.server.diff.DiffWebLinksProvider;
 import com.google.gerrit.server.git.LargeObjectException;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.patch.PatchScriptFactory;
@@ -60,10 +51,7 @@
 import com.google.gerrit.server.project.ProjectState;
 import com.google.inject.Inject;
 import java.io.IOException;
-import java.util.List;
-import java.util.Set;
 import java.util.concurrent.TimeUnit;
-import org.eclipse.jgit.diff.Edit;
 import org.kohsuke.args4j.CmdLineException;
 import org.kohsuke.args4j.CmdLineParser;
 import org.kohsuke.args4j.NamedOptionDef;
@@ -76,17 +64,6 @@
 public class GetDiff implements RestReadView<FileResource> {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
-  private static final ImmutableMap<Patch.ChangeType, ChangeType> CHANGE_TYPE =
-      Maps.immutableEnumMap(
-          new ImmutableMap.Builder<Patch.ChangeType, ChangeType>()
-              .put(Patch.ChangeType.ADDED, ChangeType.ADDED)
-              .put(Patch.ChangeType.MODIFIED, ChangeType.MODIFIED)
-              .put(Patch.ChangeType.DELETED, ChangeType.DELETED)
-              .put(Patch.ChangeType.RENAMED, ChangeType.RENAMED)
-              .put(Patch.ChangeType.COPIED, ChangeType.COPIED)
-              .put(Patch.ChangeType.REWRITE, ChangeType.REWRITE)
-              .build());
-
   private final ProjectCache projectCache;
   private final PatchScriptFactory.Factory patchScriptFactoryFactory;
   private final Revisions revisions;
@@ -164,111 +141,18 @@
       psf.setLoadHistory(false);
       psf.setLoadComments(context != DiffPreferencesInfo.WHOLE_FILE_CONTEXT);
       PatchScript ps = psf.call();
-      ContentCollector contentCollector = new ContentCollector(ps);
-      Set<Edit> editsDueToRebase = ps.getEditsDueToRebase();
-      for (Edit edit : ps.getEdits()) {
-        logger.atFine().log("next edit = %s", edit);
-
-        if (edit.getType() == Edit.Type.EMPTY) {
-          logger.atFine().log("skip empty edit");
-          continue;
-        }
-        contentCollector.addCommon(edit.getBeginA());
-
-        checkState(
-            contentCollector.nextA == edit.getBeginA(),
-            "nextA = %s; want %s",
-            contentCollector.nextA,
-            edit.getBeginA());
-        checkState(
-            contentCollector.nextB == edit.getBeginB(),
-            "nextB = %s; want %s",
-            contentCollector.nextB,
-            edit.getBeginB());
-        switch (edit.getType()) {
-          case DELETE:
-          case INSERT:
-          case REPLACE:
-            List<Edit> internalEdit =
-                edit instanceof ReplaceEdit ? ((ReplaceEdit) edit).getInternalEdits() : null;
-            boolean dueToRebase = editsDueToRebase.contains(edit);
-            contentCollector.addDiff(edit.getEndA(), edit.getEndB(), internalEdit, dueToRebase);
-            break;
-          case EMPTY:
-          default:
-            throw new IllegalStateException();
-        }
-      }
-      contentCollector.addCommon(ps.getA().size());
-
-      ProjectState state = projectCache.get(resource.getRevision().getChange().getProject());
-
-      DiffInfo result = new DiffInfo();
-      String revA = basePatchSet != null ? basePatchSet.refName() : ps.getFileInfoA().commitId;
-      String revB =
-          resource.getRevision().getEdit().isPresent()
-              ? resource.getRevision().getEdit().get().getRefName()
-              : resource.getRevision().getPatchSet().refName();
-      logger.atFine().log("revA = %s, revB = %s", revA, revB);
-
-      ImmutableList<DiffWebLinkInfo> links =
-          webLinks.getDiffLinks(
-              state.getName(),
-              resource.getPatchKey().patchSetId().changeId().get(),
-              basePatchSet != null ? basePatchSet.id().get() : null,
-              revA,
+      Project.NameKey projectName = resource.getRevision().getChange().getProject();
+      ProjectState state = projectCache.get(projectName);
+      DiffSide sideA =
+          DiffSide.create(
+              ps.getFileInfoA(),
               MoreObjects.firstNonNull(ps.getOldName(), ps.getNewName()),
-              resource.getPatchKey().patchSetId().get(),
-              revB,
-              ps.getNewName());
-      result.webLinks = links.isEmpty() ? null : links;
-
-      if (ps.isBinary()) {
-        result.binary = true;
-      }
-      if (ps.getDisplayMethodA() != DisplayMethod.NONE) {
-        result.metaA = new FileMeta();
-        result.metaA.name = MoreObjects.firstNonNull(ps.getOldName(), ps.getNewName());
-        result.metaA.contentType =
-            FileContentUtil.resolveContentType(
-                state, result.metaA.name, ps.getFileModeA(), ps.getMimeTypeA());
-        result.metaA.lines = ps.getA().size();
-        result.metaA.webLinks = getFileWebLinks(state.getProject(), revA, result.metaA.name);
-        result.metaA.commitId = ps.getFileInfoA().commitId;
-      }
-
-      if (ps.getDisplayMethodB() != DisplayMethod.NONE) {
-        result.metaB = new FileMeta();
-        result.metaB.name = ps.getNewName();
-        result.metaB.contentType =
-            FileContentUtil.resolveContentType(
-                state, result.metaB.name, ps.getFileModeB(), ps.getMimeTypeB());
-        result.metaB.lines = ps.getB().size();
-        result.metaB.webLinks = getFileWebLinks(state.getProject(), revB, result.metaB.name);
-        result.metaB.commitId = ps.getFileInfoB().commitId;
-      }
-
-      if (intraline) {
-        if (ps.hasIntralineTimeout()) {
-          result.intralineStatus = IntraLineStatus.TIMEOUT;
-        } else if (ps.hasIntralineFailure()) {
-          result.intralineStatus = IntraLineStatus.FAILURE;
-        } else {
-          result.intralineStatus = IntraLineStatus.OK;
-        }
-        logger.atFine().log("intralineStatus = %s", result.intralineStatus);
-      }
-
-      result.changeType = CHANGE_TYPE.get(ps.getChangeType());
-      logger.atFine().log("changeType = %s", result.changeType);
-      if (result.changeType == null) {
-        throw new IllegalStateException("unknown change type: " + ps.getChangeType());
-      }
-
-      if (ps.getPatchHeader().size() > 0) {
-        result.diffHeader = ps.getPatchHeader();
-      }
-      result.content = contentCollector.lines;
+              DiffSide.Type.SIDE_A);
+      DiffSide sideB = DiffSide.create(ps.getFileInfoB(), ps.getNewName(), DiffSide.Type.SIDE_B);
+      DiffWebLinksProvider webLinksProvider =
+          new DiffWebLinksProviderImpl(sideA, sideB, projectName, basePatchSet, webLinks, resource);
+      DiffInfoCreator diffInfoCreator = new DiffInfoCreator(state, webLinksProvider, intraline);
+      DiffInfo result = diffInfoCreator.create(ps, sideA, sideB);
 
       Response<DiffInfo> r = Response.ok(result);
       if (resource.isCacheable()) {
@@ -282,9 +166,69 @@
     }
   }
 
-  private List<WebLinkInfo> getFileWebLinks(Project project, String rev, String file) {
-    ImmutableList<WebLinkInfo> links = webLinks.getFileLinks(project.getName(), rev, file);
-    return links.isEmpty() ? null : links;
+  private static class DiffWebLinksProviderImpl implements DiffWebLinksProvider {
+
+    private final WebLinks webLinks;
+    private final Project.NameKey projectName;
+    private final DiffSide sideA;
+    private final DiffSide sideB;
+    private final String revA;
+    private final String revB;
+    private final FileResource resource;
+    @Nullable private final PatchSet basePatchSet;
+
+    DiffWebLinksProviderImpl(
+        DiffSide sideA,
+        DiffSide sideB,
+        Project.NameKey projectName,
+        @Nullable PatchSet basePatchSet,
+        WebLinks webLinks,
+        FileResource resource) {
+      this.projectName = projectName;
+      this.webLinks = webLinks;
+      this.basePatchSet = basePatchSet;
+      this.resource = resource;
+      this.sideA = sideA;
+      this.sideB = sideB;
+
+      revA = basePatchSet != null ? basePatchSet.refName() : sideA.fileInfo().commitId;
+
+      RevisionResource revision = resource.getRevision();
+      revB =
+          revision
+              .getEdit()
+              .map(edit -> edit.getRefName())
+              .orElseGet(() -> revision.getPatchSet().refName());
+
+      logger.atFine().log("revA = %s, revB = %s", revA, revB);
+    }
+
+    @Override
+    public ImmutableList<DiffWebLinkInfo> getDiffLinks() {
+      return webLinks.getDiffLinks(
+          projectName.get(),
+          resource.getPatchKey().patchSetId().changeId().get(),
+          basePatchSet != null ? basePatchSet.id().get() : null,
+          revA,
+          sideA.fileName(),
+          resource.getPatchKey().patchSetId().get(),
+          revB,
+          sideB.fileName());
+    }
+
+    @Override
+    public ImmutableList<WebLinkInfo> getFileWebLinks(DiffSide.Type type) {
+      String rev;
+      DiffSide side;
+      if (type == DiffSide.Type.SIDE_A) {
+        rev = revA;
+        side = sideA;
+      } else {
+        rev = revB;
+        side = sideB;
+      }
+      return webLinks.getFileLinks(projectName.get(), rev, side.fileName());
+    }
   }
 
   public GetDiff setBase(String base) {
@@ -312,141 +256,6 @@
     return this;
   }
 
-  private static class ContentCollector {
-    final List<ContentEntry> lines;
-    final SparseFileContent fileA;
-    final SparseFileContent fileB;
-    final boolean ignoreWS;
-
-    int nextA;
-    int nextB;
-
-    ContentCollector(PatchScript ps) {
-      lines = Lists.newArrayListWithExpectedSize(ps.getEdits().size() + 2);
-      fileA = ps.getA();
-      fileB = ps.getB();
-      ignoreWS = ps.isIgnoreWhitespace();
-    }
-
-    void addCommon(int end) {
-      logger.atFine().log("addCommon: end = %d", end);
-
-      end = Math.min(end, fileA.size());
-      logger.atFine().log("end = %d", end);
-
-      if (nextA >= end) {
-        logger.atFine().log("nextA >= end: nextA = %d, end = %d", nextA, end);
-        return;
-      }
-
-      while (nextA < end) {
-        logger.atFine().log("nextA < end: nextA = %d, end = %d", nextA, end);
-
-        if (!fileA.contains(nextA)) {
-          logger.atFine().log("fileA does not contain nextA: nextA = %d", nextA);
-
-          int endRegion = Math.min(end, nextA == 0 ? fileA.first() : fileA.next(nextA - 1));
-          int len = endRegion - nextA;
-          entry().skip = len;
-          nextA = endRegion;
-          nextB += len;
-
-          logger.atFine().log("setting: nextA = %d, nextB = %d", nextA, nextB);
-          continue;
-        }
-
-        ContentEntry e = null;
-        for (int i = nextA; i == nextA && i < end; i = fileA.next(i), nextA++, nextB++) {
-          if (ignoreWS && fileB.contains(nextB)) {
-            if (e == null || e.common == null) {
-              logger.atFine().log("create new common entry: nextA = %d, nextB = %d", nextA, nextB);
-              e = entry();
-              e.a = Lists.newArrayListWithCapacity(end - nextA);
-              e.b = Lists.newArrayListWithCapacity(end - nextA);
-              e.common = true;
-            }
-            e.a.add(fileA.get(nextA));
-            e.b.add(fileB.get(nextB));
-          } else {
-            if (e == null || e.common != null) {
-              logger.atFine().log(
-                  "create new non-common entry: nextA = %d, nextB = %d", nextA, nextB);
-              e = entry();
-              e.ab = Lists.newArrayListWithCapacity(end - nextA);
-            }
-            e.ab.add(fileA.get(nextA));
-          }
-        }
-        logger.atFine().log("nextA = %d, nextB = %d", nextA, nextB);
-      }
-    }
-
-    void addDiff(int endA, int endB, List<Edit> internalEdit, boolean dueToRebase) {
-      logger.atFine().log(
-          "addDiff: endA = %d, endB = %d, numberOfInternalEdits = %d, dueToRebase = %s",
-          endA, endB, internalEdit != null ? internalEdit.size() : 0, dueToRebase);
-
-      int lenA = endA - nextA;
-      int lenB = endB - nextB;
-      logger.atFine().log("lenA = %d, lenB = %d", lenA, lenB);
-      checkState(lenA > 0 || lenB > 0);
-
-      logger.atFine().log("create non-common entry");
-      ContentEntry e = entry();
-      if (lenA > 0) {
-        logger.atFine().log("lenA > 0: lenA = %d", lenA);
-        e.a = Lists.newArrayListWithCapacity(lenA);
-        for (; nextA < endA; nextA++) {
-          e.a.add(fileA.get(nextA));
-        }
-      }
-      if (lenB > 0) {
-        logger.atFine().log("lenB > 0: lenB = %d", lenB);
-        e.b = Lists.newArrayListWithCapacity(lenB);
-        for (; nextB < endB; nextB++) {
-          e.b.add(fileB.get(nextB));
-        }
-      }
-      if (internalEdit != null && !internalEdit.isEmpty()) {
-        logger.atFine().log("processing internal edits");
-
-        e.editA = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
-        e.editB = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
-        int lastA = 0;
-        int lastB = 0;
-        for (Edit edit : internalEdit) {
-          logger.atFine().log("internal edit = %s", edit);
-
-          if (edit.getBeginA() != edit.getEndA()) {
-            logger.atFine().log(
-                "edit.getBeginA() != edit.getEndA(): edit.getBeginA() = %d, edit.getEndA() = %d",
-                edit.getBeginA(), edit.getEndA());
-            e.editA.add(
-                ImmutableList.of(edit.getBeginA() - lastA, edit.getEndA() - edit.getBeginA()));
-            lastA = edit.getEndA();
-            logger.atFine().log("lastA = %d", lastA);
-          }
-          if (edit.getBeginB() != edit.getEndB()) {
-            logger.atFine().log(
-                "edit.getBeginB() != edit.getEndB(): edit.getBeginB() = %d, edit.getEndB() = %d",
-                edit.getBeginB(), edit.getEndB());
-            e.editB.add(
-                ImmutableList.of(edit.getBeginB() - lastB, edit.getEndB() - edit.getBeginB()));
-            lastB = edit.getEndB();
-            logger.atFine().log("lastB = %d", lastB);
-          }
-        }
-      }
-      e.dueToRebase = dueToRebase ? true : null;
-    }
-
-    private ContentEntry entry() {
-      ContentEntry e = new ContentEntry();
-      lines.add(e);
-      return e;
-    }
-  }
-
   @Deprecated
   enum IgnoreWhitespace {
     NONE(DiffPreferencesInfo.Whitespace.IGNORE_NONE),
@@ -462,6 +271,7 @@
   }
 
   public static class ContextOptionHandler extends OptionHandler<Short> {
+
     public ContextOptionHandler(CmdLineParser parser, OptionDef option, Setter<Short> setter) {
       super(parser, option, setter);
     }
diff --git a/java/com/google/gerrit/server/restapi/change/Mergeable.java b/java/com/google/gerrit/server/restapi/change/Mergeable.java
index 9b17ed6..cce8923 100644
--- a/java/com/google/gerrit/server/restapi/change/Mergeable.java
+++ b/java/com/google/gerrit/server/restapi/change/Mergeable.java
@@ -17,7 +17,6 @@
 import com.google.gerrit.common.data.SubmitTypeRecord;
 import com.google.gerrit.entities.Change;
 import com.google.gerrit.entities.PatchSet;
-import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.extensions.client.SubmitType;
 import com.google.gerrit.extensions.common.MergeableInfo;
 import com.google.gerrit.extensions.restapi.AuthException;
@@ -133,10 +132,10 @@
     return Response.ok(result);
   }
 
-  private SubmitType getSubmitType(ChangeData cd) {
+  private SubmitType getSubmitType(ChangeData cd) throws ResourceConflictException {
     SubmitTypeRecord rec = submitRuleEvaluator.getSubmitType(cd);
     if (rec.status != SubmitTypeRecord.Status.OK) {
-      throw new StorageException("Submit type rule failed: " + rec);
+      throw new ResourceConflictException("submit type rule error: " + rec.errorMessage);
     }
     return rec.type;
   }
diff --git a/java/com/google/gerrit/server/restapi/project/CheckMergeability.java b/java/com/google/gerrit/server/restapi/project/CheckMergeability.java
index 69a6da8..4864fde 100644
--- a/java/com/google/gerrit/server/restapi/project/CheckMergeability.java
+++ b/java/com/google/gerrit/server/restapi/project/CheckMergeability.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.restapi.project;
 
+import com.google.gerrit.exceptions.InvalidMergeStrategyException;
 import com.google.gerrit.extensions.client.SubmitType;
 import com.google.gerrit.extensions.common.MergeableInfo;
 import com.google.gerrit.extensions.restapi.BadRequestException;
@@ -120,7 +121,7 @@
           result.conflicts = ((ResolveMerger) m).getUnmergedPaths();
         }
       }
-    } catch (IllegalArgumentException e) {
+    } catch (InvalidMergeStrategyException e) {
       throw new BadRequestException(e.getMessage());
     }
     return Response.ok(result);
diff --git a/java/com/google/gerrit/server/restapi/project/CreateBranch.java b/java/com/google/gerrit/server/restapi/project/CreateBranch.java
index 56948c1..67213c5 100644
--- a/java/com/google/gerrit/server/restapi/project/CreateBranch.java
+++ b/java/com/google/gerrit/server/restapi/project/CreateBranch.java
@@ -16,6 +16,7 @@
 
 import static com.google.gerrit.entities.RefNames.isConfigRef;
 
+import com.google.common.base.Strings;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.entities.RefNames;
@@ -93,7 +94,10 @@
     if (input.ref != null && !ref.equals(input.ref)) {
       throw new BadRequestException("ref must match URL");
     }
-    if (input.revision == null) {
+    if (input.revision != null) {
+      input.revision = input.revision.trim();
+    }
+    if (Strings.isNullOrEmpty(input.revision)) {
       input.revision = Constants.HEAD;
     }
     while (ref.startsWith("/")) {
diff --git a/java/com/google/gerrit/server/restapi/project/CreateTag.java b/java/com/google/gerrit/server/restapi/project/CreateTag.java
index dca6e9a..8fdf5e4 100644
--- a/java/com/google/gerrit/server/restapi/project/CreateTag.java
+++ b/java/com/google/gerrit/server/restapi/project/CreateTag.java
@@ -88,7 +88,10 @@
     if (input.ref != null && !ref.equals(input.ref)) {
       throw new BadRequestException("ref must match URL");
     }
-    if (input.revision == null) {
+    if (input.revision != null) {
+      input.revision = input.revision.trim();
+    }
+    if (Strings.isNullOrEmpty(input.revision)) {
       input.revision = Constants.HEAD;
     }
 
diff --git a/java/com/google/gerrit/server/update/RetryHelper.java b/java/com/google/gerrit/server/update/RetryHelper.java
index 4f9a67c..f3636c9 100644
--- a/java/com/google/gerrit/server/update/RetryHelper.java
+++ b/java/com/google/gerrit/server/update/RetryHelper.java
@@ -335,6 +335,12 @@
                 if (retryWithTraceOnFailure
                     && opts.retryWithTrace().isPresent()
                     && opts.retryWithTrace().get().test(t)) {
+                  // Exception hooks may identify exceptions for which retrying with trace should be
+                  // skipped.
+                  if (exceptionHooks.stream().anyMatch(h -> h.skipRetryWithTrace(t))) {
+                    return false;
+                  }
+
                   String caller = opts.caller().orElse("N/A");
                   String cause = formatCause(t);
                   if (!traceContext.isTracing()) {
diff --git a/javatests/com/google/gerrit/acceptance/api/change/AbandonIT.java b/javatests/com/google/gerrit/acceptance/api/change/AbandonIT.java
index abfc23d..7ecbe69 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/AbandonIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/AbandonIT.java
@@ -179,15 +179,15 @@
     assertThat(toChangeNumbers(query("is:abandoned"))).containsExactly(id4);
   }
 
+  /**
+   * When indexMergeable is disabled then the abandonIfMergeable option is ineffective and the auto
+   * abandon behaves as though it were set to its default value (true).
+   */
   @Test
   @UseClockStep
   @GerritConfig(name = "changeCleanup.abandonAfter", value = "1w")
   @GerritConfig(name = "changeCleanup.abandonIfMergeable", value = "false")
   @GerritConfig(name = "index.change.indexMergeable", value = "false")
-  /**
-   * When indexMergeable is disabled then the abandonIfMergeable option is ineffective and the auto
-   * abandon behaves as though it were set to its default value (true).
-   */
   public void abandonedIfMergeableWhenMergeableOperatorIsDisabled() throws Exception {
     ObjectId initial = repo().exactRef(HEAD).getLeaf().getObjectId();
 
diff --git a/javatests/com/google/gerrit/acceptance/rest/project/CreateBranchIT.java b/javatests/com/google/gerrit/acceptance/rest/project/CreateBranchIT.java
index e5ef5ba..85d383e 100644
--- a/javatests/com/google/gerrit/acceptance/rest/project/CreateBranchIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/project/CreateBranchIT.java
@@ -36,9 +36,11 @@
 import com.google.gerrit.extensions.api.projects.BranchInfo;
 import com.google.gerrit.extensions.api.projects.BranchInput;
 import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.ResourceConflictException;
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.inject.Inject;
+import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -146,6 +148,116 @@
         "Not allowed to create group branch.");
   }
 
+  @Test
+  public void createWithRevision() throws Exception {
+    RevCommit revision = projectOperations.project(project).getHead("master");
+
+    // update master so that points to a different revision than the revision on which we create the
+    // new branch
+    pushTo("refs/heads/master");
+    assertThat(projectOperations.project(project).getHead("master")).isNotEqualTo(revision);
+
+    BranchInput input = new BranchInput();
+    input.revision = revision.name();
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(revision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch())).isEqualTo(revision);
+  }
+
+  @Test
+  public void createWithoutSpecifyingRevision() throws Exception {
+    // If revision is not specified, the branch is created based on HEAD, which points to master.
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    BranchInput input = new BranchInput();
+    input.revision = null;
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(expectedRevision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch()))
+        .isEqualTo(expectedRevision);
+  }
+
+  @Test
+  public void createWithEmptyRevision() throws Exception {
+    // If revision is not specified, the branch is created based on HEAD, which points to master.
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    BranchInput input = new BranchInput();
+    input.revision = "";
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(expectedRevision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch()))
+        .isEqualTo(expectedRevision);
+  }
+
+  @Test
+  public void createRevisionIsTrimmed() throws Exception {
+    RevCommit revision = projectOperations.project(project).getHead("master");
+
+    BranchInput input = new BranchInput();
+    input.revision = "\t" + revision.name();
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(revision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch())).isEqualTo(revision);
+  }
+
+  @Test
+  public void createWithBranchNameAsRevision() throws Exception {
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    BranchInput input = new BranchInput();
+    input.revision = "master";
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(expectedRevision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch()))
+        .isEqualTo(expectedRevision);
+  }
+
+  @Test
+  public void createWithFullBranchNameAsRevision() throws Exception {
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    BranchInput input = new BranchInput();
+    input.revision = "refs/heads/master";
+    BranchInfo created = branch(testBranch).create(input).get();
+    assertThat(created.ref).isEqualTo(testBranch.branch());
+    assertThat(created.revision).isEqualTo(expectedRevision.name());
+    assertThat(projectOperations.project(project).getHead(testBranch.branch()))
+        .isEqualTo(expectedRevision);
+  }
+
+  @Test
+  public void cannotCreateWithNonExistingBranchNameAsRevision() throws Exception {
+    assertCreateFails(
+        testBranch,
+        "refs/heads/non-existing",
+        BadRequestException.class,
+        "invalid revision \"refs/heads/non-existing\"");
+  }
+
+  @Test
+  public void cannotCreateWithNonExistingRevision() throws Exception {
+    assertCreateFails(
+        testBranch,
+        "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
+        BadRequestException.class,
+        "invalid revision \"deadbeefdeadbeefdeadbeefdeadbeefdeadbeef\"");
+  }
+
+  @Test
+  public void cannotCreateWithInvalidRevision() throws Exception {
+    assertCreateFails(
+        testBranch,
+        "invalid\trevision",
+        BadRequestException.class,
+        "invalid revision \"invalid\trevision\"");
+  }
+
   private void blockCreateReference() throws Exception {
     projectOperations
         .project(project)
diff --git a/javatests/com/google/gerrit/acceptance/rest/project/TagsIT.java b/javatests/com/google/gerrit/acceptance/rest/project/TagsIT.java
index 3d1a148..3becb81 100644
--- a/javatests/com/google/gerrit/acceptance/rest/project/TagsIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/project/TagsIT.java
@@ -41,6 +41,7 @@
 import com.google.inject.Inject;
 import java.sql.Timestamp;
 import java.util.List;
+import org.eclipse.jgit.revwalk.RevCommit;
 import org.junit.Test;
 
 @NoHttpd
@@ -357,6 +358,53 @@
     assertThat(thrown).hasMessageThat().contains("Invalid base revision");
   }
 
+  @Test
+  public void noBaseRevision() throws Exception {
+    grantTagPermissions();
+
+    // If revision is not specified, the tag is created based on HEAD, which points to master.
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    TagInput input = new TagInput();
+    input.ref = "test";
+    input.revision = null;
+
+    TagInfo result = tag(input.ref).create(input).get();
+    assertThat(result.ref).isEqualTo(R_TAGS + input.ref);
+    assertThat(result.revision).isEqualTo(expectedRevision.name());
+  }
+
+  @Test
+  public void emptyBaseRevision() throws Exception {
+    grantTagPermissions();
+
+    // If revision is not specified, the tag is created based on HEAD, which points to master.
+    RevCommit expectedRevision = projectOperations.project(project).getHead("master");
+
+    TagInput input = new TagInput();
+    input.ref = "test";
+    input.revision = "";
+
+    TagInfo result = tag(input.ref).create(input).get();
+    assertThat(result.ref).isEqualTo(R_TAGS + input.ref);
+    assertThat(result.revision).isEqualTo(expectedRevision.name());
+  }
+
+  @Test
+  public void baseRevisionIsTrimmed() throws Exception {
+    grantTagPermissions();
+
+    RevCommit revision = projectOperations.project(project).getHead("master");
+
+    TagInput input = new TagInput();
+    input.ref = "test";
+    input.revision = "\t" + revision.name();
+
+    TagInfo result = tag(input.ref).create(input).get();
+    assertThat(result.ref).isEqualTo(R_TAGS + input.ref);
+    assertThat(result.revision).isEqualTo(revision.name());
+  }
+
   private void assertTagList(FluentIterable<String> expected, List<TagInfo> actual)
       throws Exception {
     assertThat(actual).hasSize(expected.size());
diff --git a/javatests/com/google/gerrit/elasticsearch/BUILD b/javatests/com/google/gerrit/elasticsearch/BUILD
index 955930b..6521166 100644
--- a/javatests/com/google/gerrit/elasticsearch/BUILD
+++ b/javatests/com/google/gerrit/elasticsearch/BUILD
@@ -30,6 +30,11 @@
     "//lib:jgit",
 ]
 
+HTTP_TEST_DEPS = [
+    "//lib/httpcomponents:httpasyncclient",
+    "//lib/httpcomponents:httpclient",
+]
+
 QUERY_TESTS_DEP = "//javatests/com/google/gerrit/server/query/%s:abstract_query_tests"
 
 TYPES = [
@@ -66,7 +71,7 @@
     size = "large",
     srcs = [src],
     tags = ELASTICSEARCH_TAGS,
-    deps = ELASTICSEARCH_DEPS + [QUERY_TESTS_DEP % name],
+    deps = ELASTICSEARCH_DEPS + [QUERY_TESTS_DEP % name] + HTTP_TEST_DEPS,
 ) for name, src in ELASTICSEARCH_TESTS_V6.items()]
 
 [junit_tests(
@@ -74,10 +79,7 @@
     size = "large",
     srcs = [src],
     tags = ELASTICSEARCH_TAGS,
-    deps = ELASTICSEARCH_DEPS + [QUERY_TESTS_DEP % name] + [
-        "//lib/httpcomponents:httpasyncclient",
-        "//lib/httpcomponents:httpclient",
-    ],
+    deps = ELASTICSEARCH_DEPS + [QUERY_TESTS_DEP % name] + HTTP_TEST_DEPS,
 ) for name, src in ELASTICSEARCH_TESTS_V7.items()]
 
 junit_tests(
diff --git a/javatests/com/google/gerrit/integration/git/BUILD b/javatests/com/google/gerrit/integration/git/BUILD
index 6a6f5ad..4184f1f 100644
--- a/javatests/com/google/gerrit/integration/git/BUILD
+++ b/javatests/com/google/gerrit/integration/git/BUILD
@@ -3,5 +3,5 @@
 acceptance_tests(
     srcs = glob(["*IT.java"]),
     group = "git",
-    labels = ["git"],
+    labels = ["git-protocol-v2"],
 )
diff --git a/javatests/com/google/gerrit/integration/git/GitProtocolV2IT.java b/javatests/com/google/gerrit/integration/git/GitProtocolV2IT.java
index 22981f0..8577c16 100644
--- a/javatests/com/google/gerrit/integration/git/GitProtocolV2IT.java
+++ b/javatests/com/google/gerrit/integration/git/GitProtocolV2IT.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.integration.git;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allow;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.deny;
 import static java.nio.charset.StandardCharsets.UTF_8;
@@ -30,9 +29,13 @@
 import com.google.gerrit.acceptance.UseSsh;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.common.data.Permission;
+import com.google.gerrit.entities.Change;
+import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.Project;
+import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.api.GerritApi;
 import com.google.gerrit.extensions.common.ChangeInput;
+import com.google.gerrit.server.config.AllProjectsName;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.group.SystemGroupBackend;
 import com.google.inject.Inject;
@@ -40,14 +43,20 @@
 import java.net.InetSocketAddress;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.Constants;
+import org.junit.BeforeClass;
 import org.junit.Test;
 
 @UseSsh
 public class GitProtocolV2IT extends StandaloneSiteTest {
+  private static final String ADMIN_PASSWORD = "secret";
   private final String[] SSH_KEYGEN_CMD =
       new String[] {"ssh-keygen", "-t", "rsa", "-q", "-P", "", "-f"};
   private final String[] GIT_LS_REMOTE =
       new String[] {"git", "-c", "protocol.version=2", "ls-remote", "-o", "trace=12345"};
+  private final String[] GIT_CLONE_MIRROR =
+      new String[] {"git", "-c", "protocol.version=2", "clone", "--mirror"};
+  private final String[] GIT_FETCH = new String[] {"git", "-c", "protocol.version=2", "fetch"};
+  private final String[] GIT_INIT = new String[] {"git", "init"};
   private final String GIT_SSH_COMMAND =
       "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i";
 
@@ -56,16 +65,21 @@
   @Inject private ProjectOperations projectOperations;
   @Inject private @TestSshServerAddress InetSocketAddress sshAddress;
   @Inject private @GerritServerConfig Config config;
+  @Inject private AllProjectsName allProjectsName;
 
-  @Test
-  public void testGitWireProtocolV2WithSsh() throws Exception {
+  @BeforeClass
+  public static void assertGitClientVersion() throws Exception {
     // Minimum required git-core version that supports wire protocol v2 is 2.18.0
     GitClientVersion requiredGitVersion = new GitClientVersion(2, 18, 0);
     GitClientVersion actualGitVersion =
-        new GitClientVersion(execute(ImmutableList.of("git", "version")));
-    // If not found, test succeeds with assumption violation
-    assume().that(actualGitVersion).isAtLeast(requiredGitVersion);
+        new GitClientVersion(execute(ImmutableList.of("git", "version"), new File("/")));
+    // If git client version cannot be updated, consider to skip this tests. Due to
+    // an existing issue in bazel, JUnit assumption violation feature cannot be used.
+    assertThat(actualGitVersion).isAtLeast(requiredGitVersion);
+  }
 
+  @Test
+  public void testGitWireProtocolV2WithSsh() throws Exception {
     try (ServerContext ctx = startServer()) {
       ctx.getInjector().injectMembers(this);
 
@@ -122,7 +136,7 @@
               .commit;
 
       // Prepare new change on secret branch
-      in = new ChangeInput(project.get(), "secret", "Test secret change");
+      in = new ChangeInput(project.get(), ADMIN_PASSWORD, "Test secret change");
       in.newBranch = true;
 
       // Create new change and retrieve SHA1 for the created patch set
@@ -193,9 +207,137 @@
     }
   }
 
+  @Test
+  public void testGitWireProtocolV2HidesRefMetaConfig() throws Exception {
+    try (ServerContext ctx = startServer()) {
+      ctx.getInjector().injectMembers(this);
+      String url = config.getString("gerrit", null, "canonicalweburl");
+
+      // Create project
+      Project.NameKey allRefsVisibleProject = Project.nameKey("all-refs-visible");
+      gApi.projects().create(allRefsVisibleProject.get());
+
+      // Set protocol.version=2 in target repository
+      execute(
+          ImmutableList.of("git", "config", "protocol.version", "2"),
+          sitePaths
+              .site_path
+              .resolve("git")
+              .resolve(allRefsVisibleProject.get() + Constants.DOT_GIT)
+              .toFile());
+
+      // Set up project permission to allow reading all refs
+      projectOperations
+          .project(allRefsVisibleProject)
+          .forUpdate()
+          .add(allow(Permission.READ).ref("refs/heads/*").group(SystemGroupBackend.ANONYMOUS_USERS))
+          .add(
+              allow(Permission.READ)
+                  .ref("refs/changes/*")
+                  .group(SystemGroupBackend.ANONYMOUS_USERS))
+          .update();
+
+      // Create new change and retrieve refs for the created patch set
+      ChangeInput visibleChangeIn =
+          new ChangeInput(allRefsVisibleProject.get(), "master", "Test public change");
+      visibleChangeIn.newBranch = true;
+      int visibleChangeNumber = gApi.changes().create(visibleChangeIn).info()._number;
+      Change.Id changeId = Change.id(visibleChangeNumber);
+      String visibleChangeNumberRef = RefNames.patchSetRef(PatchSet.id(changeId, 1));
+      String visibleChangeNumberMetaRef = RefNames.changeMetaRef(changeId);
+
+      // Read refs from target repository using git wire protocol v2 over HTTP anonymously
+      String outAnonymousLsRemote =
+          execute(
+              ImmutableList.<String>builder()
+                  .add(GIT_CLONE_MIRROR)
+                  .add(url + "/" + allRefsVisibleProject.get())
+                  .build(),
+              ImmutableMap.of("GIT_TRACE_PACKET", "1"));
+
+      assertThat(outAnonymousLsRemote).contains("git< version 2");
+      assertThat(outAnonymousLsRemote).doesNotContain(RefNames.REFS_CONFIG);
+      assertThat(outAnonymousLsRemote).contains(visibleChangeNumberRef);
+      assertThat(outAnonymousLsRemote).contains(visibleChangeNumberMetaRef);
+    }
+  }
+
+  @Test
+  public void testGitWireProtocolV2FetchIndividualRef() throws Exception {
+    try (ServerContext ctx = startServer()) {
+      ctx.getInjector().injectMembers(this);
+
+      // Setup admin password
+      gApi.accounts().id(admin.username()).setHttpPassword(ADMIN_PASSWORD);
+
+      // Get authenticated Git/HTTP URL
+      String urlWithCredentials =
+          config
+              .getString("gerrit", null, "canonicalweburl")
+              .replace("http://", "http://" + admin.username() + ":" + ADMIN_PASSWORD + "@");
+
+      // Create project
+      Project.NameKey privateProject = Project.nameKey("private-project");
+      gApi.projects().create(privateProject.get());
+
+      // Set protocol.version=2 in target repository
+      execute(
+          ImmutableList.of("git", "config", "protocol.version", "2"),
+          sitePaths
+              .site_path
+              .resolve("git")
+              .resolve(privateProject.get() + Constants.DOT_GIT)
+              .toFile());
+
+      // Disallow general read permissions for anonymous users
+      projectOperations
+          .project(allProjectsName)
+          .forUpdate()
+          .add(deny(Permission.READ).ref("refs/*").group(SystemGroupBackend.ANONYMOUS_USERS))
+          .add(
+              allow(Permission.READ)
+                  .ref("refs/heads/master")
+                  .group(SystemGroupBackend.REGISTERED_USERS))
+          .update();
+
+      // Set up project permission to allow registered users fetching changes/*
+      projectOperations
+          .project(privateProject)
+          .forUpdate()
+          .add(
+              allow(Permission.READ)
+                  .ref("refs/changes/*")
+                  .group(SystemGroupBackend.REGISTERED_USERS))
+          .update();
+
+      // Create new change and retrieve refs for the created patch set
+      ChangeInput visibleChangeIn =
+          new ChangeInput(privateProject.get(), "master", "Test private change");
+      visibleChangeIn.newBranch = true;
+      int visibleChangeNumber = gApi.changes().create(visibleChangeIn).info()._number;
+      Change.Id changeId = Change.id(visibleChangeNumber);
+      String visibleChangeNumberRef = RefNames.patchSetRef(PatchSet.id(changeId, 1));
+
+      // Fetch a single ref using git wire protocol v2 over HTTP with authentication
+      execute(GIT_INIT);
+
+      String outFetchRef =
+          execute(
+              ImmutableList.<String>builder()
+                  .add(GIT_FETCH)
+                  .add(urlWithCredentials + "/" + privateProject.get())
+                  .add(visibleChangeNumberRef)
+                  .build(),
+              ImmutableMap.of("GIT_TRACE_PACKET", "1"));
+
+      assertThat(outFetchRef).contains("git< version 2");
+      assertThat(outFetchRef).contains(visibleChangeNumberRef);
+    }
+  }
+
   private void setUpUserAuthentication(String username) throws Exception {
     // Assign HTTP password to user
-    gApi.accounts().id(username).setHttpPassword("secret");
+    gApi.accounts().id(username).setHttpPassword(ADMIN_PASSWORD);
 
     // Generate private/public key for user
     execute(
@@ -221,6 +363,10 @@
     assertThat(out).contains(commit);
   }
 
+  private String execute(String... cmds) throws Exception {
+    return execute(ImmutableList.<String>builder().add(cmds).build());
+  }
+
   private String execute(ImmutableList<String> cmd) throws Exception {
     return execute(cmd, sitePaths.data_dir.toFile(), ImmutableMap.of());
   }
diff --git a/javatests/com/google/gerrit/prettify/BUILD b/javatests/com/google/gerrit/prettify/BUILD
new file mode 100644
index 0000000..0eb7cee
--- /dev/null
+++ b/javatests/com/google/gerrit/prettify/BUILD
@@ -0,0 +1,13 @@
+load("//tools/bzl:junit.bzl", "junit_tests")
+
+junit_tests(
+    name = "prettify_tests",
+    srcs = glob(["**/*.java"]),
+    deps = [
+        "//java/com/google/gerrit/prettify:server",
+        "//java/com/google/gerrit/prettify/common/testing",
+        "//java/com/google/gerrit/testing:gerrit-test-util",
+        "//lib:guava",
+        "//lib/truth",
+    ],
+)
diff --git a/javatests/com/google/gerrit/prettify/common/SparseFileContentBuilderTest.java b/javatests/com/google/gerrit/prettify/common/SparseFileContentBuilderTest.java
new file mode 100644
index 0000000..a751d50
--- /dev/null
+++ b/javatests/com/google/gerrit/prettify/common/SparseFileContentBuilderTest.java
@@ -0,0 +1,170 @@
+// Copyright (C) 2019 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.prettify.common;
+
+import static com.google.gerrit.prettify.common.testing.SparseFileContentSubject.assertThat;
+import static com.google.gerrit.testing.GerritJUnit.assertThrows;
+
+import com.google.common.collect.ImmutableMap;
+import org.junit.Ignore;
+import org.junit.Test;
+
+public class SparseFileContentBuilderTest {
+
+  @Test
+  public void addLineWithNegativeNumber() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(10);
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(-1, "First line"));
+
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(-5, "First line"));
+  }
+
+  @Test
+  @Ignore
+  public void addLineNumberZeroFileSize() {
+    // Temporary ignore - see comments in SparseFileContentBuilder.build() method
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(0);
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(0, "First line"));
+  }
+
+  @Test
+  @Ignore
+  public void addLineNumberNonZeroFileSize() {
+    // Temporary ignore - see comments in SparseFileContentBuilder.build() method
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(5);
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(5, "First line"));
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(6, "First line"));
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(7, "First line"));
+  }
+
+  @Test
+  public void addLineIncorrectOrder() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(5);
+
+    builder.addLine(0, "First line");
+    builder.addLine(1, "Second line");
+    builder.addLine(3, "Third line");
+    builder.addLine(4, "Fourth line");
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(4, "Other Line"));
+
+    assertThrows(IllegalArgumentException.class, () -> builder.addLine(2, "Other Line"));
+  }
+
+  @Test
+  public void emptyContentZeroSize() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(0);
+
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(0);
+    assertThat(content).getRangesCount().isEqualTo(0);
+    assertThat(content).lines().isEmpty();
+  }
+
+  @Test
+  public void emptyContentNonZeroSize() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(4);
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(4);
+    assertThat(content).getRangesCount().isEqualTo(0);
+    assertThat(content).lines().isEmpty();
+  }
+
+  @Test
+  public void oneLineContentLineNumberZero() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(1);
+
+    builder.addLine(0, "First line");
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(1);
+    assertThat(content).getRangesCount().isEqualTo(1);
+    assertThat(content).lines().containsExactlyEntriesIn(ImmutableMap.of(0, "First line"));
+  }
+
+  @Test
+  public void oneLineContentLineNumberNotZero() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(6);
+
+    builder.addLine(5, "First line");
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(6);
+    assertThat(content).getRangesCount().isEqualTo(1);
+    assertThat(content).lines().containsExactlyEntriesIn(ImmutableMap.of(5, "First line"));
+  }
+
+  @Test
+  public void multiLineContinuousContentStartingFromZero() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(5);
+
+    builder.addLine(0, "First line");
+    builder.addLine(1, "Second line");
+    builder.addLine(2, "Third line");
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(5);
+    assertThat(content).getRangesCount().isEqualTo(1);
+    assertThat(content)
+        .lines()
+        .containsExactlyEntriesIn(
+            ImmutableMap.of(
+                0, "First line",
+                1, "Second line",
+                2, "Third line"));
+  }
+
+  @Test
+  public void multiLineContentStartingFromNonZeroLine() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(8);
+
+    builder.addLine(5, "First line");
+    builder.addLine(6, "Second line");
+    builder.addLine(7, "Third line");
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(8);
+    assertThat(content).getRangesCount().isEqualTo(1);
+    assertThat(content)
+        .lines()
+        .containsExactlyEntriesIn(
+            ImmutableMap.of(
+                5, "First line",
+                6, "Second line",
+                7, "Third line"));
+  }
+
+  @Test
+  public void multiLineContentWithGaps() {
+    SparseFileContentBuilder builder = new SparseFileContentBuilder(10000);
+    builder.addLine(0, "First line");
+    builder.addLine(1, "Second line");
+    builder.addLine(3, "Third line");
+    builder.addLine(4, "Fourth line");
+    builder.addLine(5, "Fifth line");
+    builder.addLine(6, "Sixth line");
+    builder.addLine(10, "Seventh line");
+    SparseFileContent content = builder.build();
+    assertThat(content).getSize().isEqualTo(10000);
+    assertThat(content).getRangesCount().isEqualTo(3);
+    assertThat(content)
+        .lines()
+        .containsExactlyEntriesIn(
+            ImmutableMap.builder()
+                .put(0, "First line")
+                .put(1, "Second line")
+                .put(3, "Third line")
+                .put(4, "Fourth line")
+                .put(5, "Fifth line")
+                .put(6, "Sixth line")
+                .put(10, "Seventh line")
+                .build());
+  }
+}
diff --git a/modules/jgit b/modules/jgit
index 0356613..a7e454b 160000
--- a/modules/jgit
+++ b/modules/jgit
@@ -1 +1 @@
-Subproject commit 0356613f48ebee2e3d2d65780e71d9e0b43a752e
+Subproject commit a7e454bc51d359c2d46b19fd559f770cad8fd7d4
diff --git a/plugins/gitiles b/plugins/gitiles
index 3531010..22b8e24 160000
--- a/plugins/gitiles
+++ b/plugins/gitiles
@@ -1 +1 @@
-Subproject commit 3531010e04d9d548fe1fd93662ca85ae25d4a9a6
+Subproject commit 22b8e242b5eaa9eae817b776bc862b096479ceaa
diff --git a/plugins/replication b/plugins/replication
index ef5ffc7..b3ed3c8 160000
--- a/plugins/replication
+++ b/plugins/replication
@@ -1 +1 @@
-Subproject commit ef5ffc7508627f8c2f86e03c556703aa28c2f134
+Subproject commit b3ed3c8f9a8bab51beed794de5be8fd6da44231a
diff --git a/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior.html b/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior.html
index 8f9bf00..67e4ca6 100644
--- a/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior.html
+++ b/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior.html
@@ -81,6 +81,12 @@
       return path;
     },
 
+    isMagicPath(path) {
+      return !!path &&
+          (path === Gerrit.PathListBehavior.COMMIT_MESSAGE_PATH || path ===
+              Gerrit.PathListBehavior.MERGE_LIST_PATH);
+    },
+
     computeTruncatedPath(path) {
       return Gerrit.PathListBehavior.truncatePath(
           Gerrit.PathListBehavior.computeDisplayPath(path));
diff --git a/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior_test.html b/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior_test.html
index 924c98c..12b981c 100644
--- a/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior_test.html
+++ b/polygerrit-ui/app/behaviors/gr-path-list-behavior/gr-path-list-behavior_test.html
@@ -56,6 +56,14 @@
       assert.equal(name('/MERGE_LIST'), 'Merge list');
     });
 
+    test('isMagicPath', () => {
+      const isMagic = Gerrit.PathListBehavior.isMagicPath;
+      assert.isFalse(isMagic(undefined));
+      assert.isFalse(isMagic('/foo.cc'));
+      assert.isTrue(isMagic('/COMMIT_MSG'));
+      assert.isTrue(isMagic('/MERGE_LIST'));
+    });
+
     test('truncatePath with long path should add ellipsis', () => {
       const truncatePath = Gerrit.PathListBehavior.truncatePath;
       let path = 'level1/level2/level3/level4/file.js';
diff --git a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view_test.html b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view_test.html
index e6eef75..04bdab7 100644
--- a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view_test.html
+++ b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view_test.html
@@ -197,7 +197,10 @@
         assert.equal(Polymer.dom(element.root)
             .querySelectorAll('.sectionTitle').length, 3);
         assert.equal(element.$$('.breadcrumbText').innerText, 'Test Repo');
-        assert.equal(element.$$('#pageSelect').items.length, 6);
+        assert.equal(
+            element.shadowRoot.querySelector('#pageSelect').items.length,
+            6
+        );
         done();
       });
     });
@@ -439,13 +442,16 @@
       element.reload().then(() => {
         assert.deepEqual(element._filteredLinks, expectedFilteredLinks);
         assert.deepEqual(element._subsectionLinks, expectedSubsectionLinks);
-        assert.equal(element.$$('#pageSelect').value, 'repoaccess');
+        assert.equal(
+            element.shadowRoot.querySelector('#pageSelect').value,
+            'repoaccess'
+        );
         assert.isTrue(element._selectedIsCurrentPage.calledOnce);
         // Doesn't trigger navigation from the page select menu.
         assert.isFalse(Gerrit.Nav.navigateToRelativeUrl.called);
 
         // When explicitly changed, navigation is called
-        element.$$('#pageSelect').value = 'repo';
+        element.shadowRoot.querySelector('#pageSelect').value = 'repo';
         assert.isTrue(element._selectedIsCurrentPage.calledTwice);
         assert.isTrue(Gerrit.Nav.navigateToRelativeUrl.calledOnce);
         done();
diff --git a/polygerrit-ui/app/elements/admin/gr-permission/gr-permission_test.html b/polygerrit-ui/app/elements/admin/gr-permission/gr-permission_test.html
index 6cb7e4a..7919b28 100644
--- a/polygerrit-ui/app/elements/admin/gr-permission/gr-permission_test.html
+++ b/polygerrit-ui/app/elements/admin/gr-permission/gr-permission_test.html
@@ -385,7 +385,8 @@
 
         assert.isFalse(element._originalExclusiveValue);
         assert.isNotOk(element.permission.value.modified);
-        MockInteractions.tap(element.$$('#exclusiveToggle'));
+        MockInteractions.tap(element.shadowRoot
+            .querySelector('#exclusiveToggle'));
         flushAsynchronousOperations();
         assert.isTrue(element.permission.value.exclusive);
         assert.isTrue(element.permission.value.modified);
@@ -405,21 +406,25 @@
       });
 
       test('Exclusive hidden for owner permission', () => {
-        assert.equal(getComputedStyle(element.$$('#exclusiveToggle')).display,
-            'flex');
+        assert.equal(getComputedStyle(element.shadowRoot
+            .querySelector('#exclusiveToggle')).display,
+        'flex');
         element.set(['permission', 'id'], 'owner');
         flushAsynchronousOperations();
-        assert.equal(getComputedStyle(element.$$('#exclusiveToggle')).display,
-            'none');
+        assert.equal(getComputedStyle(element.shadowRoot
+            .querySelector('#exclusiveToggle')).display,
+        'none');
       });
 
       test('Exclusive hidden for any global permissions', () => {
-        assert.equal(getComputedStyle(element.$$('#exclusiveToggle')).display,
-            'flex');
+        assert.equal(getComputedStyle(element.shadowRoot
+            .querySelector('#exclusiveToggle')).display,
+        'flex');
         element.section = 'GLOBAL_CAPABILITIES';
         flushAsynchronousOperations();
-        assert.equal(getComputedStyle(element.$$('#exclusiveToggle')).display,
-            'none');
+        assert.equal(getComputedStyle(element.shadowRoot
+            .querySelector('#exclusiveToggle')).display,
+        'none');
       });
     });
   });
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-access/gr-repo-access_test.html b/polygerrit-ui/app/elements/admin/gr-repo-access/gr-repo-access_test.html
index 90eaba5..fc7dea8 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-access/gr-repo-access_test.html
+++ b/polygerrit-ui/app/elements/admin/gr-repo-access/gr-repo-access_test.html
@@ -282,7 +282,8 @@
           id: 'test-project',
         };
         flushAsynchronousOperations();
-        assert.equal(getComputedStyle(element.$$('#editInheritFromInput'))
+        assert.equal(getComputedStyle(element.shadowRoot
+            .querySelector('#editInheritFromInput'))
             .display, 'none');
 
         MockInteractions.tap(element.$.editBtn);
@@ -300,7 +301,8 @@
           assert.notEqual(getComputedStyle(element.$.saveBtn).display, 'none');
           assert.isTrue(element.$.saveBtn.disabled);
         }
-        assert.notEqual(getComputedStyle(element.$$('#editInheritFromInput'))
+        assert.notEqual(getComputedStyle(element.shadowRoot
+            .querySelector('#editInheritFromInput'))
             .display, 'none');
 
         // Save button should be enabled after access is modified
@@ -365,7 +367,7 @@
           id: 'test-project',
         };
         flushAsynchronousOperations();
-        element.$$('#editInheritFromInput').fire('commit');
+        element.shadowRoot.querySelector('#editInheritFromInput').fire('commit');
         sandbox.spy(element, '_handleAccessModified');
         element.fire('access-modified');
         assert.isTrue(element._handleAccessModified.called);
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
index 6703651..0817762 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
@@ -269,25 +269,6 @@
           Do you really want to delete the edit?
         </div>
       </gr-dialog>
-      <gr-dialog
-        id="showRevertSubmissionChangesDialog"
-        class="confirmDialog"
-        confirm-label="Close"
-        cancel-label=''
-        on-confirm="_handleShowRevertSubmissionChangesConfirm">
-        <div class="header" slot="header">
-          Reverted Changes
-        </div>
-        <div class="main" slot="main">
-          <template is="dom-repeat" items="[[_revertChanges]]">
-            <div>
-              <a href$="[[item.link]]" target="_blank">
-                Change [[item._number]]
-              </a>
-            </div>
-          </template>
-        </div>
-      </gr-dialog>
     </gr-overlay>
     <gr-js-api-interface id="jsAPI"></gr-js-api-interface>
     <gr-rest-api-interface id="restAPI"></gr-rest-api-interface>
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
index 8ad2a06..9d2854a 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
@@ -420,10 +420,6 @@
           type: Boolean,
           value: true,
         },
-        _revertChanges: {
-          type: Array,
-          value: [],
-        },
       };
     }
 
@@ -1262,7 +1258,6 @@
     _handleResponse(action, response) {
       if (!response) { return; }
       return this.$.restAPI.getResponseObject(response).then(obj => {
-        let revertChanges = [];
         switch (action.__key) {
           case ChangeActions.REVERT:
             this._waitForChangeReachable(obj._number)
@@ -1288,27 +1283,11 @@
             Gerrit.Nav.navigateToChange(this.change);
             break;
           case ChangeActions.REVERT_SUBMISSION:
-            revertChanges = obj.revert_changes || [];
-            revertChanges = revertChanges.map(change => {
-              change.link = '/q/' + encodeURIComponent(change.change_id);
-              return change;
-            });
-            // list of reverted changes can never be 0
-            if (revertChanges.length === 1) {
-              // redirect to the change if only 1 change is reverted
-              const change = revertChanges[0];
-              this._waitForChangeReachable(change._number).then(success => {
-                if (success) {
-                  Gerrit.Nav.navigateToChange(change);
-                } else {
-                  console.error('Change ' + change._number + ' not reachable');
-                }
-              });
-            } else {
-              // show multiple reverted changes in a dialog
-              this._revertChanges = revertChanges;
-              this._showActionDialog(this.$.showRevertSubmissionChangesDialog);
-            }
+            if (!obj.revert_changes || !obj.revert_changes.length) return;
+            /* If there is only 1 change then gerrit will automatically
+               redirect to that change */
+            Gerrit.Nav.navigateToSearchQuery('topic: ' +
+                obj.revert_changes[0].topic);
             break;
           default:
             this.dispatchEvent(new CustomEvent('reload-change',
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
index 532c573..50f6fb0 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
@@ -466,7 +466,9 @@
         element._handleDeleteEditTap();
         assert.isFalse(element.$.confirmDeleteEditDialog.hidden);
         MockInteractions.tap(
-            element.$$('#confirmDeleteEditDialog').$$('gr-button[primary]'));
+            element.shadowRoot
+                .querySelector('#confirmDeleteEditDialog')
+                .$$('gr-button[primary]'));
         flushAsynchronousOperations();
 
         assert.equal(fireActionStub.lastCall.args[0], '/edit');
@@ -980,9 +982,12 @@
 
       test('shows confirm dialog', () => {
         element._handleDeleteTap();
-        assert.isFalse(element.$$('#confirmDeleteDialog').hidden);
+        assert.isFalse(element.shadowRoot
+            .querySelector('#confirmDeleteDialog').hidden);
         MockInteractions.tap(
-            element.$$('#confirmDeleteDialog').$$('gr-button[primary]'));
+            element.shadowRoot
+                .querySelector('#confirmDeleteDialog')
+                .$$('gr-button[primary]'));
         flushAsynchronousOperations();
         assert.isTrue(fireActionStub.calledWith('/', deleteAction, false));
       });
@@ -990,9 +995,12 @@
       test('hides delete confirm on cancel', () => {
         element._handleDeleteTap();
         MockInteractions.tap(
-            element.$$('#confirmDeleteDialog').$$('gr-button:not([primary])'));
+            element.shadowRoot
+                .querySelector('#confirmDeleteDialog')
+                .$$('gr-button:not([primary])'));
         flushAsynchronousOperations();
-        assert.isTrue(element.$$('#confirmDeleteDialog').hidden);
+        assert.isTrue(element.shadowRoot
+            .querySelector('#confirmDeleteDialog').hidden);
         assert.isFalse(fireActionStub.called);
       });
     });
@@ -1438,7 +1446,6 @@
 
       suite('happy path', () => {
         let sendStub;
-        let waitForChangeReachableStub;
         setup(() => {
           sandbox.stub(element, 'fetchChangeUpdates')
               .returns(Promise.resolve({isLatest: true}));
@@ -1446,8 +1453,6 @@
               .returns(Promise.resolve({}));
           getResponseObjectStub = sandbox.stub(element.$.restAPI,
               'getResponseObject');
-          waitForChangeReachableStub = sandbox.stub(element,
-              '_waitForChangeReachable').returns(Promise.resolve(true));
           sandbox.stub(Gerrit.Nav,
               'navigateToChange').returns(Promise.resolve(true));
         });
@@ -1463,12 +1468,15 @@
         });
 
         suite('single changes revert', () => {
+          let navigateToSearchQueryStub;
           setup(() => {
             getResponseObjectStub
                 .returns(Promise.resolve({revert_changes: [
                   {change_id: 12345},
                 ]}));
             showActionDialogStub = sandbox.stub(element, '_showActionDialog');
+            navigateToSearchQueryStub = sandbox.stub(Gerrit.Nav,
+                'navigateToSearchQuery');
           });
 
           test('revert submission single change', done => {
@@ -1476,7 +1484,7 @@
                 '/revert_submission', false, cleanup).then(res => {
               element._handleResponse({__key: 'revert_submission'}, {}).
                   then(() => {
-                    assert.isTrue(waitForChangeReachableStub.called);
+                    assert.isTrue(navigateToSearchQueryStub.called);
                     done();
                   });
             });
@@ -1485,12 +1493,16 @@
 
         suite('multiple changes revert', () => {
           let showActionDialogStub;
+          let navigateToSearchQueryStub;
           setup(() => {
             getResponseObjectStub
                 .returns(Promise.resolve({revert_changes: [
-                  {change_id: 12345}, {change_id: 23456},
+                  {change_id: 12345, topic: 'T'},
+                  {change_id: 23456, topic: 'T'},
                 ]}));
             showActionDialogStub = sandbox.stub(element, '_showActionDialog');
+            navigateToSearchQueryStub = sandbox.stub(Gerrit.Nav,
+                'navigateToSearchQuery');
           });
 
           test('revert submission multiple change', done => {
@@ -1498,7 +1510,9 @@
                 '/revert_submission', false, cleanup).then(res => {
               element._handleResponse({__key: 'revert_submission'}, {}).then(
                   () => {
-                    assert.isTrue(showActionDialogStub.called);
+                    assert.isFalse(showActionDialogStub.called);
+                    assert.isTrue(navigateToSearchQueryStub.calledWith(
+                        'topic: T'));
                     done();
                   });
             });
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
index 5de378b..b9e9e6c 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
@@ -437,7 +437,8 @@
     }
 
     _handleFileTabChange(e) {
-      const selectedIndex = this.$$('#primaryTabs').selected;
+      const selectedIndex = this.shadowRoot
+          .querySelector('#primaryTabs').selected;
       this._showFileTabContent = selectedIndex === 0;
       // Initial tab is the static files list.
       const newSelectedTab =
@@ -458,8 +459,8 @@
         console.warn(e.detail.tab + ' tab not found');
         return;
       }
-      this.$$('#primaryTabs').selected = idx + 1;
-      this.$$('#primaryTabs').scrollIntoView();
+      this.shadowRoot.querySelector('#primaryTabs').selected = idx + 1;
+      this.shadowRoot.querySelector('#primaryTabs').scrollIntoView();
       this.$.reporting.reportInteraction('show-tab', e.detail.tab);
     }
 
@@ -799,7 +800,7 @@
       // Selected has to be set after the paper-tabs are visible because
       // the selected underline depends on calculations made by the browser.
       this.$.commentTabs.selected = 0;
-      const primaryTabs = this.$$('#primaryTabs');
+      const primaryTabs = this.shadowRoot.querySelector('#primaryTabs');
       if (primaryTabs) primaryTabs.selected = 0;
     }
 
diff --git a/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog.js b/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog.js
index ab849de..9329ba5 100644
--- a/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog.js
+++ b/polygerrit-ui/app/elements/change/gr-download-dialog/gr-download-dialog.js
@@ -68,7 +68,8 @@
     }
 
     getFocusStops() {
-      const links = this.$$('#archives').querySelectorAll('a');
+      const links = this.shadowRoot
+          .querySelector('#archives').querySelectorAll('a');
       return {
         start: this.$.closeButton,
         end: links[links.length - 1],
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
index ea7ea8f..10efaff 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
@@ -216,8 +216,8 @@
     test('expand/collapse buttons are toggled correctly', () => {
       element.shownFileCount = 10;
       flushAsynchronousOperations();
-      const expandBtn = element.$$('#expandBtn');
-      const collapseBtn = element.$$('#collapseBtn');
+      const expandBtn = element.shadowRoot.querySelector('#expandBtn');
+      const collapseBtn = element.shadowRoot.querySelector('#collapseBtn');
       assert.notEqual(getComputedStyle(expandBtn).display, 'none');
       assert.equal(getComputedStyle(collapseBtn).display, 'none');
       element.filesExpanded = GrFileListConstants.FilesExpandedState.SOME;
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.html b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.html
index 318633d..0a7f1ce 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.html
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.html
@@ -116,6 +116,9 @@
         cursor: pointer;
         flex: 1;
         text-decoration: none;
+        /* Wrap it into multiple lines if too long. */
+        white-space: normal;
+        word-break: break-word;
       }
       .path:hover :first-child {
         text-decoration: underline;
@@ -197,10 +200,6 @@
       .truncatedFileName {
         display: none;
       }
-      .expanded .fullFileName {
-        white-space: normal;
-        word-wrap: break-word;
-      }
       .mobile {
         display: none;
       }
@@ -247,7 +246,9 @@
         margin: -2px 0;
         padding: var(--spacing-s) 0;
       }
-      @media screen and (max-width: 50em) {
+
+      /** small screen breakpoint: 768px */
+      @media screen and (max-width: 55em) {
         .desktop {
           display: none;
         }
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
index fb57164..9943192 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
@@ -339,9 +339,9 @@
     }
 
     _calculatePatchChange(files) {
-      const magicFilesExcluded = files.filter(files => {
-        return files.__path !== '/COMMIT_MSG' && files.__path !== '/MERGE_LIST';
-      });
+      const magicFilesExcluded = files.filter(files =>
+        !this.isMagicPath(files.__path)
+      );
 
       return magicFilesExcluded.reduce((acc, obj) => {
         const inserted = obj.lines_inserted ? obj.lines_inserted : 0;
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
index 9caf13d..b0747f4 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
@@ -231,7 +231,8 @@
           .concat(_.times(11, randomMessage));
       flushAsynchronousOperations();
 
-      MockInteractions.tap(element.$$('#collapse-messages')); // Expand all.
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages')); // Expand all.
       flushAsynchronousOperations();
 
       let messages = getMessages();
@@ -255,8 +256,10 @@
           .concat(_.times(11, randomMessage));
       flushAsynchronousOperations();
 
-      MockInteractions.tap(element.$$('#collapse-messages')); // Expand all.
-      MockInteractions.tap(element.$$('#collapse-messages')); // Collapse all.
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages')); // Expand all.
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages')); // Collapse all.
       flushAsynchronousOperations();
 
       let messages = getMessages();
@@ -283,13 +286,15 @@
       MockInteractions.tap(allMessageEls[1]);
       assert.isTrue(allMessageEls[1]._expanded);
 
-      MockInteractions.tap(element.$$('#collapse-messages'));
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages'));
       allMessageEls = getMessages();
       for (const message of allMessageEls) {
         assert.isTrue(message._expanded);
       }
 
-      MockInteractions.tap(element.$$('#collapse-messages'));
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages'));
       allMessageEls = getMessages();
       for (const message of allMessageEls) {
         assert.isFalse(message._expanded);
@@ -297,28 +302,33 @@
     });
 
     test('expand/collapse from external keypress', () => {
-      MockInteractions.tap(element.$$('#collapse-messages'));
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages'));
       let allMessageEls = getMessages();
       for (const message of allMessageEls) {
         assert.isTrue(message._expanded);
       }
 
       // Expand/collapse all text also changes.
-      assert.equal(element.$$('#collapse-messages').textContent.trim(),
-          'Collapse all');
+      assert.equal(element.shadowRoot
+          .querySelector('#collapse-messages').textContent.trim(),
+      'Collapse all');
 
-      MockInteractions.tap(element.$$('#collapse-messages'));
+      MockInteractions.tap(element.shadowRoot
+          .querySelector('#collapse-messages'));
       allMessageEls = getMessages();
       for (const message of allMessageEls) {
         assert.isFalse(message._expanded);
       }
       // Expand/collapse all text also changes.
-      assert.equal(element.$$('#collapse-messages').textContent.trim(),
-          'Expand all');
+      assert.equal(element.shadowRoot
+          .querySelector('#collapse-messages').textContent.trim(),
+      'Expand all');
     });
 
     test('hide messages does not appear when no automated messages', () => {
-      assert.isOk(element.$$('#automatedMessageToggleContainer[hidden]'));
+      assert.isOk(element.shadowRoot
+          .querySelector('#automatedMessageToggleContainer[hidden]'));
     });
 
     test('scroll to message', () => {
@@ -476,7 +486,8 @@
     });
 
     test('hide autogenerated button is not hidden', () => {
-      assert.isNotOk(element.$$('#automatedMessageToggle[hidden]'));
+      assert.isNotOk(element.shadowRoot
+          .querySelector('#automatedMessageToggle[hidden]'));
     });
 
     test('autogenerated messages are not hidden initially', () => {
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
index badd62a..e44f669 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
@@ -187,7 +187,7 @@
     });
 
     test('keep drafts with reply', done => {
-      MockInteractions.tap(element.$$('#includeComments'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#includeComments'));
       assert.equal(element._includeComments, false);
 
       // Async tick is needed because iron-selector content is distributed and
@@ -460,7 +460,8 @@
       flushAsynchronousOperations();
       assert.isFalse(element._reviewersMutated);
       assert.isTrue(element.$.ccs.allowAnyInput);
-      assert.isFalse(element.$$('#reviewers').allowAnyInput);
+      assert.isFalse(element.shadowRoot
+          .querySelector('#reviewers').allowAnyInput);
       element.$.ccs.dispatchEvent(new CustomEvent('account-text-changed',
           {bubbles: true, composed: true}));
       assert.isTrue(element._reviewersMutated);
diff --git a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
index d169728..3f2f4bd 100644
--- a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
+++ b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
@@ -24,7 +24,6 @@
     CATEGORY_RPC: 'RPC Timing',
     // Reported events - alphabetize below.
     APP_STARTED: 'App Started',
-    PAGE_LOADED: 'Page Loaded',
   };
 
   // Plugin-related reporting constants.
@@ -298,38 +297,21 @@
         console.error('pageLoaded should be called after window.onload');
         this.async(this.pageLoaded, 100);
       } else {
-        const loadTime = this.performanceTiming.loadEventEnd -
+        const perfEvents = Object.keys(this.performanceTiming.toJSON());
+        perfEvents.forEach(
+            eventName => this._reportPerformanceTiming(eventName)
+        );
+      }
+    },
+
+    _reportPerformanceTiming(eventName) {
+      const eventTiming = this.performanceTiming[eventName];
+      if (eventTiming > 0) {
+        const elapsedTime = eventTiming -
             this.performanceTiming.navigationStart;
+        // NavResTime - Navigation and resource timings.
         this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-            TIMING.PAGE_LOADED, loadTime, true);
-
-        const requestStart = this.performanceTiming.requestStart -
-            this.performanceTiming.navigationStart;
-        this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-            'requestStart', requestStart, true);
-
-        const responseEnd = this.performanceTiming.responseEnd -
-            this.performanceTiming.navigationStart;
-        this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-            'responseEnd', responseEnd, true);
-
-        const domLoading = this.performanceTiming.domLoading -
-          this.performanceTiming.navigationStart;
-        this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-            'domLoading', domLoading, true);
-
-        const domContentLoadedEventStart =
-          this.performanceTiming.domContentLoadedEventStart -
-          this.performanceTiming.navigationStart;
-        this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-            'domContentLoadedEventStart', domContentLoadedEventStart, true);
-
-        if (this.performanceTiming.redirectEnd > 0) {
-          const redirectEnd = this.performanceTiming.redirectEnd -
-              this.performanceTiming.navigationStart;
-          this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-              'redirectEnd', redirectEnd, true);
-        }
+            `NavResTime - ${eventName}`, elapsedTime, true);
       }
     },
 
diff --git a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
index c2c0297..430b41e 100644
--- a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
+++ b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
@@ -52,6 +52,7 @@
         navigationStart: 1,
         loadEventEnd: 2,
       };
+      fakePerformance.toJSON = () => fakePerformance;
       sinon.stub(element, 'performanceTiming',
           {get() { return fakePerformance; }});
       sandbox.stub(element, 'reporter');
@@ -83,7 +84,7 @@
       element.pageLoaded();
       assert.isTrue(
           element.reporter.calledWithExactly(
-              'timing-report', 'UI Latency', 'Page Loaded',
+              'timing-report', 'UI Latency', 'NavResTime - loadEventEnd',
               fakePerformance.loadEventEnd - fakePerformance.navigationStart,
               true)
       );
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor.js b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor.js
index 039a99fa..fc4173c 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor.js
@@ -35,9 +35,9 @@
   const LEFT_SIDE_CLASS = 'target-side-left';
   const RIGHT_SIDE_CLASS = 'target-side-right';
 
-  class GrDiffCursor extends Polymer.GestureEventListeners(
-      Polymer.LegacyElementMixin(
-          Polymer.Element)) {
+  class GrDiffCursor extends Polymer.mixinBehaviors([Gerrit.FireBehavior],
+      Polymer.GestureEventListeners(
+          Polymer.LegacyElementMixin(Polymer.Element))) {
     static get is() { return 'gr-diff-cursor'; }
 
     static get properties() {
@@ -105,6 +105,23 @@
       ];
     }
 
+    ready() {
+      super.ready();
+      Polymer.RenderStatus.afterNextRender(this, () => {
+        /*
+        This represents the diff cursor is ready for interaction coming from
+        client components. It is more then Polymer "ready" lifecycle, as no
+        "ready" events are automatically fired by Polymer, it means
+        the cursor is completely interactable - in this case attached and
+        painted on the page. We name it "ready" instead of "rendered" as the
+        long-term goal is to make gr-diff-cursor a javascript class - not a DOM
+        element with an actual lifecycle. This will be triggered only once
+        per element.
+        */
+        this.fire('ready', null, {bubbles: false});
+      });
+    }
+
     attached() {
       super.attached();
       // Catch when users are scrolling as the view loads.
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.html b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.html
index 626ab33..dff9e79 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.html
@@ -42,6 +42,12 @@
   </template>
 </test-fixture>
 
+<test-fixture id="empty">
+  <template>
+    <div></div>
+  </template>
+</test-fixture>
+
 <script>
   suite('gr-diff-cursor tests', () => {
     let sandbox;
@@ -370,4 +376,24 @@
       });
     });
   });
+
+  suite('gr-diff-cursor event tests', () => {
+    let sandbox;
+    let someEmptyDiv;
+
+    setup(() => {
+      sandbox = sinon.sandbox.create();
+      someEmptyDiv = fixture('empty');
+    });
+
+    teardown(() => sandbox.restore());
+
+    test('ready is fired after component is rendered', done => {
+      const cursorElement = document.createElement('gr-diff-cursor');
+      cursorElement.addEventListener('ready', () => {
+        done();
+      });
+      someEmptyDiv.appendChild(cursorElement);
+    });
+  });
 </script>
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
index 40a02a3..cd53510 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
@@ -277,7 +277,7 @@
           </span>
         </div>
         <div class="rightControls">
-          <span class$="blameLoader [[_computeBlameLoaderClass(_isImageDiff)]]">
+          <span class$="blameLoader [[_computeBlameLoaderClass(_isImageDiff, _path)]]">
             <gr-button
                 link
                 disabled="[[_isBlameLoading]]"
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
index 4c401cf..2f2b3863 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
@@ -1101,8 +1101,8 @@
           });
     }
 
-    _computeBlameLoaderClass(isImageDiff) {
-      return !isImageDiff ? 'show' : '';
+    _computeBlameLoaderClass(isImageDiff, path) {
+      return !this.isMagicPath(path) && !isImageDiff ? 'show' : '';
     }
 
     _getRevisionInfo(change) {
diff --git a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.html b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.html
index 2d7dc9c..b7e52a1 100644
--- a/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.html
+++ b/polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls_test.html
@@ -82,7 +82,7 @@
     });
 
     test('open', () => {
-      MockInteractions.tap(element.$$('#open'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#open'));
       element.patchNum = 1;
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element._hideAllDialogs.called);
@@ -101,7 +101,7 @@
     });
 
     test('cancel', () => {
-      MockInteractions.tap(element.$$('#open'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#open'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.openDialog.disabled);
         openAutoCcmplete.noDebounce = true;
@@ -129,7 +129,7 @@
 
     test('delete', () => {
       deleteStub.returns(Promise.resolve({ok: true}));
-      MockInteractions.tap(element.$$('#delete'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#delete'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.deleteDialog.disabled);
         assert.isFalse(queryStub.called);
@@ -152,7 +152,7 @@
 
     test('delete fails', () => {
       deleteStub.returns(Promise.resolve({ok: false}));
-      MockInteractions.tap(element.$$('#delete'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#delete'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.deleteDialog.disabled);
         assert.isFalse(queryStub.called);
@@ -173,7 +173,7 @@
     });
 
     test('cancel', () => {
-      MockInteractions.tap(element.$$('#delete'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#delete'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.deleteDialog.disabled);
         element.$.deleteDialog.querySelector('gr-autocomplete').text =
@@ -204,7 +204,7 @@
 
     test('rename', () => {
       renameStub.returns(Promise.resolve({ok: true}));
-      MockInteractions.tap(element.$$('#rename'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#rename'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.renameDialog.disabled);
         assert.isFalse(queryStub.called);
@@ -232,7 +232,7 @@
 
     test('rename fails', () => {
       renameStub.returns(Promise.resolve({ok: false}));
-      MockInteractions.tap(element.$$('#rename'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#rename'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.renameDialog.disabled);
         assert.isFalse(queryStub.called);
@@ -258,7 +258,7 @@
     });
 
     test('cancel', () => {
-      MockInteractions.tap(element.$$('#rename'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#rename'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         assert.isTrue(element.$.renameDialog.disabled);
         element.$.renameDialog.querySelector('gr-autocomplete').text =
@@ -285,13 +285,14 @@
     });
 
     test('restore hidden by default', () => {
-      assert.isTrue(element.$$('#restore').classList.contains('invisible'));
+      assert.isTrue(element.shadowRoot
+          .querySelector('#restore').classList.contains('invisible'));
     });
 
     test('restore', () => {
       restoreStub.returns(Promise.resolve({ok: true}));
       element._path = 'src/test.cpp';
-      MockInteractions.tap(element.$$('#restore'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#restore'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         MockInteractions.tap(element.$.restoreDialog.$$('gr-button[primary]'));
         flushAsynchronousOperations();
@@ -309,7 +310,7 @@
     test('restore fails', () => {
       restoreStub.returns(Promise.resolve({ok: false}));
       element._path = 'src/test.cpp';
-      MockInteractions.tap(element.$$('#restore'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#restore'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         MockInteractions.tap(element.$.restoreDialog.$$('gr-button[primary]'));
         flushAsynchronousOperations();
@@ -325,7 +326,7 @@
 
     test('cancel', () => {
       element._path = 'src/test.cpp';
-      MockInteractions.tap(element.$$('#restore'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#restore'));
       return showDialogSpy.lastCall.returnValue.then(() => {
         MockInteractions.tap(element.$.restoreDialog.$$('gr-button'));
         assert.isFalse(navStub.called);
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.html b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.html
index 89b28d5..0567777 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.html
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.html
@@ -90,6 +90,7 @@
           as="comment">
         <gr-comment
             comment="{{comment}}"
+            comments="{{comments}}"
             robot-button-disabled="[[_shouldDisableAction(_showActions, _lastComment)]]"
             change-num="[[changeNum]]"
             patch-num="[[patchNum]]"
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.js b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.js
index 8687e77..779e247 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.js
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.js
@@ -373,7 +373,7 @@
       const comment = e.detail.comment;
       const msg = comment.message;
       const quoteStr = '> ' + msg.replace(NEWLINE_PATTERN, '\n> ') + '\n\n';
-      const response = quoteStr + 'Please Fix';
+      const response = quoteStr + 'Please fix.';
       this._createReplyComment(comment, response, false, true);
     }
 
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.html b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.html
index 17e0b1f..ceadae1 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_test.html
@@ -420,7 +420,7 @@
         });
         assert.equal(drafts.length, 1);
         assert.equal(
-            drafts[0].message, '> is this a crossover episode!?\n\nPlease Fix');
+            drafts[0].message, '> is this a crossover episode!?\n\nPlease fix.');
         assert.equal(drafts[0].in_reply_to, 'baf0414d_60047215');
         assert.isTrue(drafts[0].unresolved);
         done();
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.html b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.html
index cb87bd9..d1d60f1 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.html
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.html
@@ -60,7 +60,7 @@
         display: none;
       }
       .header {
-        align-items: baseline;
+        align-items: center;
         cursor: pointer;
         display: flex;
         margin: calc(0px - var(--spacing-m)) calc(0px - var(--spacing-m)) 0 calc(0px - var(--spacing-m));
@@ -271,7 +271,7 @@
             secondary
             class$="action delete [[_computeDeleteButtonClass(_isAdmin, draft)]]"
             on-click="_handleCommentDelete">
-          (Delete)
+          <iron-icon id="icon" icon="gr-icons:delete"></iron-icon>
         </gr-button>
         <span class="date" on-click="_handleAnchorClick">
           <gr-date-formatter
@@ -348,14 +348,16 @@
         </div>
         <div class="robotActions" hidden$="[[!_showRobotActions]]">
           <template is="dom-if" if="[[isRobotComment]]">
-            <gr-button
-                link
-                secondary
-                class="action fix"
-                on-click="_handleFix"
-                disabled="[[robotButtonDisabled]]">
-              Please Fix
-            </gr-button>
+            <template is="dom-if" if="[[!_hasHumanReply]]">
+              <gr-button
+                  link
+                  secondary
+                  class="action fix"
+                  on-click="_handleFix"
+                  disabled="[[robotButtonDisabled]]">
+                Please Fix
+              </gr-button>
+            </template>
             <gr-endpoint-decorator name="robot-comment-controls">
               <gr-endpoint-param name="comment" value="[[comment]]">
               </gr-endpoint-param>
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
index 053eeee..eb4081e 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
@@ -81,6 +81,9 @@
           notify: true,
           observer: '_commentChanged',
         },
+        comments: {
+          type: Array,
+        },
         isRobotComment: {
           type: Boolean,
           value: false,
@@ -119,6 +122,7 @@
         /** @type {?} */
         projectConfig: Object,
         robotButtonDisabled: Boolean,
+        _hasHumanReply: Boolean,
         _isAdmin: {
           type: Boolean,
           value: false,
@@ -165,6 +169,7 @@
         '_loadLocalDraft(changeNum, patchNum, comment)',
         '_isRobotComment(comment)',
         '_calculateActionstoShow(showActions, isRobotComment)',
+        '_computeHasHumanReply(comment, comments.*)',
       ];
     }
 
@@ -196,14 +201,15 @@
     }
 
     get textarea() {
-      return this.$$('#editTextarea');
+      return this.shadowRoot.querySelector('#editTextarea');
     }
 
     get confirmDeleteOverlay() {
       if (!this._overlays.confirmDelete) {
         this._enableOverlay = true;
         Polymer.dom.flush();
-        this._overlays.confirmDelete = this.$$('#confirmDeleteOverlay');
+        this._overlays.confirmDelete = this.shadowRoot
+            .querySelector('#confirmDeleteOverlay');
       }
       return this._overlays.confirmDelete;
     }
@@ -212,7 +218,8 @@
       if (!this._overlays.confirmDiscard) {
         this._enableOverlay = true;
         Polymer.dom.flush();
-        this._overlays.confirmDiscard = this.$$('#confirmDiscardOverlay');
+        this._overlays.confirmDiscard = this.shadowRoot
+            .querySelector('#confirmDiscardOverlay');
       }
       return this._overlays.confirmDiscard;
     }
@@ -308,6 +315,15 @@
       }
     }
 
+    _computeHasHumanReply() {
+      if (!this.comment || !this.comments) return;
+      // hide please fix button for robot comment that has human reply
+      this._hasHumanReply = this.comments.some(c => {
+        return c.in_reply_to && c.in_reply_to === this.comment.id
+            && !c.robot_id;
+      });
+    }
+
     /**
      * @param {!Object=} opt_mixin
      *
@@ -354,7 +370,7 @@
       if (editing) {
         this.async(() => {
           Polymer.dom.flush();
-          this.textarea.putCursorAtEnd();
+          this.textarea && this.textarea.putCursorAtEnd();
         }, 1);
       }
     }
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.html b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.html
index ad8b5e4..81dfaeb 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment_test.html
@@ -867,9 +867,145 @@
         done();
       });
       element.isRobotComment = true;
+      element.comments = [element.comment];
       flushAsynchronousOperations();
 
       MockInteractions.tap(element.$$('.fix'));
     });
+
+    test('do not show Please Fix button if human reply exists', () => {
+      element.comments = [
+        {
+          robot_id: 'happy_robot_id',
+          robot_run_id: '5838406743490560',
+          fix_suggestions: [
+            {
+              fix_id: '478ff847_3bf47aaf',
+              description: 'Make the smiley happier by giving it a nose.',
+              replacements: [
+                {
+                  path: 'Documentation/config-gerrit.txt',
+                  range: {
+                    start_line: 10,
+                    start_character: 7,
+                    end_line: 10,
+                    end_character: 9,
+                  },
+                  replacement: ':-)',
+                },
+              ],
+            },
+          ],
+          author: {
+            _account_id: 1030912,
+            name: 'Alice Kober-Sotzek',
+            email: 'aliceks@google.com',
+            avatars: [
+              {
+                url: '/s32-p/photo.jpg',
+                height: 32,
+              },
+              {
+                url: '/AaAdOFzPlFI/s56-p/photo.jpg',
+                height: 56,
+              },
+              {
+                url: '/AaAdOFzPlFI/s100-p/photo.jpg',
+                height: 100,
+              },
+              {
+                url: '/AaAdOFzPlFI/s120-p/photo.jpg',
+                height: 120,
+              },
+            ],
+          },
+          patch_set: 1,
+          id: 'eb0d03fd_5e95904f',
+          line: 10,
+          updated: '2017-04-04 15:36:17.000000000',
+          message: 'This is a robot comment with a fix.',
+          unresolved: false,
+          __commentSide: 'right',
+          collapsed: false,
+        },
+        {
+          __draft: true,
+          __draftID: '0.wbrfbwj89sa',
+          __date: '2019-12-04T13:41:03.689Z',
+          path: 'Documentation/config-gerrit.txt',
+          patchNum: 1,
+          side: 'REVISION',
+          __commentSide: 'right',
+          line: 10,
+          in_reply_to: 'eb0d03fd_5e95904f',
+          message: '> This is a robot comment with a fix.\n\nPlease fix.',
+          unresolved: true,
+        },
+      ];
+      element.comment = element.comments[0];
+      flushAsynchronousOperations();
+      assert.isNull(element.$$('robotActions gr-button'));
+    });
+
+    test('show Please Fix if no human reply', () => {
+      element.comments = [
+        {
+          robot_id: 'happy_robot_id',
+          robot_run_id: '5838406743490560',
+          fix_suggestions: [
+            {
+              fix_id: '478ff847_3bf47aaf',
+              description: 'Make the smiley happier by giving it a nose.',
+              replacements: [
+                {
+                  path: 'Documentation/config-gerrit.txt',
+                  range: {
+                    start_line: 10,
+                    start_character: 7,
+                    end_line: 10,
+                    end_character: 9,
+                  },
+                  replacement: ':-)',
+                },
+              ],
+            },
+          ],
+          author: {
+            _account_id: 1030912,
+            name: 'Alice Kober-Sotzek',
+            email: 'aliceks@google.com',
+            avatars: [
+              {
+                url: '/s32-p/photo.jpg',
+                height: 32,
+              },
+              {
+                url: '/AaAdOFzPlFI/s56-p/photo.jpg',
+                height: 56,
+              },
+              {
+                url: '/AaAdOFzPlFI/s100-p/photo.jpg',
+                height: 100,
+              },
+              {
+                url: '/AaAdOFzPlFI/s120-p/photo.jpg',
+                height: 120,
+              },
+            ],
+          },
+          patch_set: 1,
+          id: 'eb0d03fd_5e95904f',
+          line: 10,
+          updated: '2017-04-04 15:36:17.000000000',
+          message: 'This is a robot comment with a fix.',
+          unresolved: false,
+          __commentSide: 'right',
+          collapsed: false,
+        },
+      ];
+      element.comment = element.comments[0];
+      flushAsynchronousOperations();
+      assert.isNotNull(element.$$('.robotActions gr-button'));
+    });
   });
 </script>
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js
index 2d66cfa..0ec3d6a 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js
@@ -50,7 +50,11 @@
       return url.pathname;
     }
     const base = Gerrit.BaseUrlBehavior.getBaseUrl();
-    const pathname = url.pathname.replace(base, '');
+    let pathname = url.pathname.replace(base, '');
+    // Load from ASSETS_PATH
+    if (window.ASSETS_PATH && url.href.includes(window.ASSETS_PATH)) {
+      pathname = url.href.replace(window.ASSETS_PATH, '');
+    }
     // Site theme is server from predefined path.
     if (pathname === '/static/gerrit-theme.html') {
       return 'gerrit-theme';
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html
index 128738d..b43796f 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html
@@ -72,6 +72,15 @@
             'gerrit-theme'
         );
       });
+
+      test('with ASSETS_PATH', () => {
+        window.ASSETS_PATH = 'http://cdn.com/2';
+        assert.equal(
+            getPluginNameFromUrl(`${window.ASSETS_PATH}/plugins/a.html`),
+            'a'
+        );
+        window.ASSETS_PATH = undefined;
+      });
     });
   });
 </script>
\ No newline at end of file
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
index 537e55b..bdce91f 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
@@ -82,6 +82,28 @@
           'http://test.com/plugins/testplugin/static/test.js');
     });
 
+    test('url for preloaded plugin without ASSETS_PATH', () => {
+      let plugin;
+      Gerrit.install(p => { plugin = p; }, '0.1',
+          'preloaded:testpluginB');
+      assert.equal(plugin.url(),
+          `${window.location.origin}/plugins/testpluginB/`);
+      assert.equal(plugin.url('/static/test.js'),
+          `${window.location.origin}/plugins/testpluginB/static/test.js`);
+    });
+
+    test('url for preloaded plugin without ASSETS_PATH', () => {
+      const oldAssetsPath = window.ASSETS_PATH;
+      window.ASSETS_PATH = 'http://test.com';
+      let plugin;
+      Gerrit.install(p => { plugin = p; }, '0.1',
+          'preloaded:testpluginC');
+      assert.equal(plugin.url(), `${window.ASSETS_PATH}/plugins/testpluginC/`);
+      assert.equal(plugin.url('/static/test.js'),
+          `${window.ASSETS_PATH}/plugins/testpluginC/static/test.js`);
+      window.ASSETS_PATH = oldAssetsPath;
+    });
+
     test('_send on failure rejects with response text', () => {
       sendStub.returns(Promise.resolve(
           {status: 400, text() { return Promise.resolve('text'); }}));
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.js
index 4be38b6..081ce55 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader.js
@@ -113,7 +113,7 @@
       this._pluginListLoaded = true;
 
       plugins.forEach(path => {
-        const url = this._urlFor(path);
+        const url = this._urlFor(path, window.ASSETS_PATH);
         // Skip if preloaded, for bundling.
         if (this.isPluginPreloaded(url)) return;
 
@@ -128,11 +128,11 @@
         });
 
         if (this._isPathEndsWith(url, '.html')) {
-          this._importHtmlPlugin(url, opts && opts[path]);
+          this._importHtmlPlugin(path, opts && opts[path]);
         } else if (this._isPathEndsWith(url, '.js')) {
-          this._loadJsPlugin(url);
+          this._loadJsPlugin(path);
         } else {
-          this._failToLoad(`Unrecognized plugin url ${url}`, url);
+          this._failToLoad(`Unrecognized plugin path ${path}`, path);
         }
       });
 
@@ -181,14 +181,15 @@
         return;
       }
 
-      const pluginObject = this.getPlugin(src);
+      const url = this._urlFor(src);
+      const pluginObject = this.getPlugin(url);
       let plugin = pluginObject && pluginObject.plugin;
       if (!plugin) {
-        plugin = new Plugin(src);
+        plugin = new Plugin(url);
       }
       try {
         callback(plugin);
-        this._pluginInstalled(src, plugin);
+        this._pluginInstalled(url, plugin);
       } catch (e) {
         this._failToLoad(`${e.name}: ${e.message}`, src);
       }
@@ -313,38 +314,79 @@
     }
 
     _importHtmlPlugin(pluginUrl, opts = {}) {
-      // onload (second param) needs to be a function. When null or undefined
-      // were passed, plugins were not loaded correctly.
+      const urlWithAP = this._urlFor(pluginUrl, window.ASSETS_PATH);
+      const urlWithoutAP = this._urlFor(pluginUrl);
+      let onerror = null;
+      if (urlWithAP !== urlWithoutAP) {
+        onerror = () => this._loadHtmlPlugin(urlWithoutAP, opts.sync);
+      }
+      this._loadHtmlPlugin(urlWithAP, opts.sync, onerror);
+    }
+
+    _loadHtmlPlugin(url, sync, onerror) {
+      if (!onerror) {
+        onerror = () => {
+          this._failToLoad(`${url} import error`, url);
+        };
+      }
+
       (Polymer.importHref || Polymer.Base.importHref)(
-          this._urlFor(pluginUrl), () => {},
-          () => this._failToLoad(`${pluginUrl} import error`, pluginUrl),
-          !opts.sync);
+          url, () => {},
+          onerror,
+          !sync);
     }
 
     _loadJsPlugin(pluginUrl) {
-      this._createScriptTag(this._urlFor(pluginUrl));
+      const urlWithAP = this._urlFor(pluginUrl, window.ASSETS_PATH);
+      const urlWithoutAP = this._urlFor(pluginUrl);
+      let onerror = null;
+      if (urlWithAP !== urlWithoutAP) {
+        onerror = () => this._createScriptTag(urlWithoutAP);
+      }
+
+      this._createScriptTag(urlWithAP, onerror);
     }
 
-    _createScriptTag(url) {
+    _createScriptTag(url, onerror) {
+      if (!onerror) {
+        onerror = () => this._failToLoad(`${url} load error`, url);
+      }
+
       const el = document.createElement('script');
       el.defer = true;
       el.setAttribute('src', url);
-      el.onerror = () => this._failToLoad(`${url} load error`, url);
+      el.onerror = onerror;
       return document.body.appendChild(el);
     }
 
-    _urlFor(pathOrUrl) {
+    _urlFor(pathOrUrl, assetsPath) {
       if (!pathOrUrl) {
         return pathOrUrl;
       }
+
+      // theme is per host, should always load from assetsPath
+      const isThemeFile = pathOrUrl.endsWith('static/gerrit-theme.html');
+      const shouldTryLoadFromAssetsPathFirst = !isThemeFile && assetsPath;
       if (pathOrUrl.startsWith(PRELOADED_PROTOCOL) ||
           pathOrUrl.startsWith('http')) {
         // Plugins are loaded from another domain or preloaded.
+        if (pathOrUrl.includes(location.host)
+          && shouldTryLoadFromAssetsPathFirst) {
+          // if is loading from host server, try replace with cdn when assetsPath provided
+          return pathOrUrl
+              .replace(location.origin, assetsPath);
+        }
         return pathOrUrl;
       }
+
       if (!pathOrUrl.startsWith('/')) {
         pathOrUrl = '/' + pathOrUrl;
       }
+
+      if (shouldTryLoadFromAssetsPathFirst) {
+        return assetsPath + pathOrUrl;
+      }
+
       return window.location.origin + getBaseUrl() + pathOrUrl;
     }
 
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.html
index 8c1ec96..151c340 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-plugin-loader_test.html
@@ -325,11 +325,11 @@
       let loadJsPluginStub;
       setup(() => {
         importHtmlPluginStub = sandbox.stub();
-        sandbox.stub(Gerrit._pluginLoader, '_importHtmlPlugin', url => {
+        sandbox.stub(Gerrit._pluginLoader, '_loadHtmlPlugin', url => {
           importHtmlPluginStub(url);
         });
         loadJsPluginStub = sandbox.stub();
-        sandbox.stub(Gerrit._pluginLoader, '_loadJsPlugin', url => {
+        sandbox.stub(Gerrit._pluginLoader, '_createScriptTag', url => {
           loadJsPluginStub(url);
         });
       });
@@ -346,8 +346,8 @@
 
         assert.isTrue(failToLoadStub.calledOnce);
         assert.isTrue(failToLoadStub.calledWithExactly(
-            `Unrecognized plugin url ${url}/foo/bar`,
-            `${url}/foo/bar`
+            'Unrecognized plugin path foo/bar',
+            'foo/bar'
         ));
       });
 
@@ -407,6 +407,72 @@
       });
     });
 
+    suite('With ASSETS_PATH', () => {
+      let importHtmlPluginStub;
+      let loadJsPluginStub;
+      setup(() => {
+        window.ASSETS_PATH = 'https://cdn.com';
+        importHtmlPluginStub = sandbox.stub();
+        sandbox.stub(Gerrit._pluginLoader, '_loadHtmlPlugin', url => {
+          importHtmlPluginStub(url);
+        });
+        loadJsPluginStub = sandbox.stub();
+        sandbox.stub(Gerrit._pluginLoader, '_createScriptTag', url => {
+          loadJsPluginStub(url);
+        });
+      });
+
+      teardown(() => {
+        window.ASSETS_PATH = '';
+      });
+
+      test('Should try load plugins from assets path instead', () => {
+        Gerrit._loadPlugins([
+          'foo/bar.js',
+          'foo/bar.html',
+        ]);
+
+        assert.isTrue(importHtmlPluginStub.calledOnce);
+        assert.isTrue(
+            importHtmlPluginStub.calledWithExactly(`https://cdn.com/foo/bar.html`)
+        );
+        assert.isTrue(loadJsPluginStub.calledOnce);
+        assert.isTrue(
+            loadJsPluginStub.calledWithExactly(`https://cdn.com/foo/bar.js`));
+      });
+
+      test('Should honor original path if exists', () => {
+        Gerrit._loadPlugins([
+          'http://e.com/foo/bar.html',
+          'http://e.com/foo/bar.js',
+        ]);
+
+        assert.isTrue(importHtmlPluginStub.calledOnce);
+        assert.isTrue(
+            importHtmlPluginStub.calledWithExactly(`http://e.com/foo/bar.html`)
+        );
+        assert.isTrue(loadJsPluginStub.calledOnce);
+        assert.isTrue(
+            loadJsPluginStub.calledWithExactly(`http://e.com/foo/bar.js`));
+      });
+
+      test('Should try replace current host with assetsPath', () => {
+        const host = window.location.origin;
+        Gerrit._loadPlugins([
+          `${host}/foo/bar.html`,
+          `${host}/foo/bar.js`,
+        ]);
+
+        assert.isTrue(importHtmlPluginStub.calledOnce);
+        assert.isTrue(
+            importHtmlPluginStub.calledWithExactly(`https://cdn.com/foo/bar.html`)
+        );
+        assert.isTrue(loadJsPluginStub.calledOnce);
+        assert.isTrue(
+            loadJsPluginStub.calledWithExactly(`https://cdn.com/foo/bar.js`));
+      });
+    });
+
     test('adds js plugins will call the body', () => {
       Gerrit._loadPlugins([
         'http://e.com/foo/bar.js',
@@ -489,12 +555,10 @@
 
       test('installing preloaded plugin', () => {
         let plugin;
-        window.ASSETS_PATH = 'http://blips.com/chitz';
         Gerrit.install(p => { plugin = p; }, '0.1', 'preloaded:foo');
         assert.strictEqual(plugin.getPluginName(), 'foo');
         assert.strictEqual(plugin.url('/some/thing.html'),
-            'http://blips.com/chitz/plugins/foo/some/thing.html');
-        delete window.ASSETS_PATH;
+            `${window.location.origin}/plugins/foo/some/thing.html`);
       });
     });
   });
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
index 6c306d9..6dc0309 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
@@ -17,8 +17,6 @@
 (function(window) {
   'use strict';
 
-  const PRELOADED_PROTOCOL = 'preloaded:';
-
   const PANEL_ENDPOINTS_MAPPING = {
     CHANGE_SCREEN_BELOW_COMMIT_INFO_BLOCK: 'change-view-integration',
     CHANGE_SCREEN_BELOW_CHANGE_INFO_BLOCK: 'change-metadata-item',
@@ -26,6 +24,7 @@
 
   // Import utils methods
   const {
+    PRELOADED_PROTOCOL,
     getPluginNameFromUrl,
     send,
   } = window._apiUtils;
@@ -66,13 +65,6 @@
 
     this._url = new URL(opt_url);
     this._name = getPluginNameFromUrl(this._url);
-    if (this._url.protocol === PRELOADED_PROTOCOL) {
-      // Original plugin URL is used in plugin assets URLs calculation.
-      const assetsBaseUrl = window.ASSETS_PATH ||
-          (window.location.origin + Gerrit.BaseUrlBehavior.getBaseUrl());
-      this._url = new URL(assetsBaseUrl + '/plugins/' + this._name +
-          '/static/' + this._name + '.js');
-    }
   }
 
   Plugin._sharedAPIElement = document.createElement('gr-js-api-interface');
@@ -139,9 +131,15 @@
 
   Plugin.prototype.url = function(opt_path) {
     const relPath = '/plugins/' + this._name + (opt_path || '/');
+    const sameOriginPath = window.location.origin +
+      `${Gerrit.BaseUrlBehavior.getBaseUrl()}${relPath}`;
     if (window.location.origin === this._url.origin) {
       // Plugin loaded from the same origin as gr-app, getBaseUrl in effect.
-      return this._url.origin + Gerrit.BaseUrlBehavior.getBaseUrl() + relPath;
+      return sameOriginPath;
+    } else if (this._url.protocol === PRELOADED_PROTOCOL) {
+      // Plugin is preloaded, load plugin with ASSETS_PATH or location.origin
+      return window.ASSETS_PATH ? `${window.ASSETS_PATH}${relPath}`
+        : sameOriginPath;
     } else {
       // Plugin loaded from assets bundle, expect assets placed along with it.
       return this._url.href.split('/plugins/' + this._name)[0] + relPath;
diff --git a/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view_test.html b/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view_test.html
index 8f87b38..f99d5d9 100644
--- a/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view_test.html
@@ -126,11 +126,13 @@
     });
 
     test('createNew link appears correctly', () => {
-      assert.isFalse(element.$$('#createNewContainer').classList
+      assert.isFalse(element.shadowRoot
+          .querySelector('#createNewContainer').classList
           .contains('show'));
       element.createNew = true;
       flushAsynchronousOperations();
-      assert.isTrue(element.$$('#createNewContainer').classList
+      assert.isTrue(element.shadowRoot
+          .querySelector('#createNewContainer').classList
           .contains('show'));
     });
 
@@ -139,7 +141,7 @@
       element.addEventListener('create-clicked', clickHandler);
       element.createNew = true;
       flushAsynchronousOperations();
-      MockInteractions.tap(element.$$('#createNew'));
+      MockInteractions.tap(element.shadowRoot.querySelector('#createNew'));
       assert.isTrue(clickHandler.called);
     });
 
diff --git a/polygerrit-ui/app/styles/themes/app-theme.html b/polygerrit-ui/app/styles/themes/app-theme.html
index 3a620d2..87230e6 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.html
+++ b/polygerrit-ui/app/styles/themes/app-theme.html
@@ -42,28 +42,34 @@
   --vote-text-color-disliked: #d32f2f;
 
   /* background colors */
+  /* primary background colors */
+  --background-color-primary: #ffffff;
+  --background-color-secondary: #f8f9fa;
+  --background-color-tertiary: #f1f3f4;
+  /* directly derived from primary background colors */
+  --chip-background-color: var(--background-color-tertiary);
+  --default-button-background-color: var(--background-color-primary);
+  --dialog-background-color: var(--background-color-primary);
+  --dropdown-background-color: var(--background-color-primary);
+  --expanded-background-color: var(--background-color-tertiary);
+  --secondary-button-background-color: var(--background-color-primary);
+  --select-background-color: var(--background-color-secondary);
+  --shell-command-background-color: var(--background-color-secondary);
+  --shell-command-decoration-background-color: var(--background-color-tertiary);
+  --table-header-background-color: var(--background-color-secondary);
+  --table-subheader-background-color: var(--background-color-tertiary);
+  --view-background-color: var(--background-color-primary);
+  /* unique background colors */
   --assignee-highlight-color: #fcfad6;
-  --chip-background-color: #eee;
   --comment-background-color: #fcfad6;
   --robot-comment-background-color: #e8f0fe;
-  --default-button-background-color: white;
-  --dialog-background-color: white;
-  --dropdown-background-color: white;
   --edit-mode-background-color: #ebf5fb;
   --emphasis-color: #fff9c4;
-  --expanded-background-color: #eee;
   --hover-background-color: rgba(161, 194, 250, 0.2);
   --primary-button-background-color: #2a66d9;
-  --secondary-button-background-color: white;
-  --select-background-color: #f8f8f8;
   --selection-background-color: rgba(161, 194, 250, 0.1);
-  --shell-command-background-color: #f5f5f5;
-  --shell-command-decoration-background-color: #ebebeb;
-  --table-header-background-color: #fafafa;
-  --table-subheader-background-color: #eaeaea;
   --tooltip-background-color: #333;
   --unresolved-comment-background-color: #fcfaa6;
-  --view-background-color: white;
   --vote-color-approved: #9fcc6b;
   --vote-color-disliked: #f7c4cb;
   --vote-color-neutral: #ebf5fb;
@@ -71,7 +77,7 @@
   --vote-color-rejected: #f7a1ad;
 
   /* misc colors */
-  --border-color: #ddd;
+  --border-color: #dadce0;
 
   /* fonts */
   --font-family: 'Roboto', -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';
@@ -103,9 +109,9 @@
   --spacing-xxl: 24px;
 
   /* header and footer */
-  --footer-background-color: #eee;
+  --footer-background-color: var(--background-color-tertiary);
   --footer-border-top: 1px solid var(--border-color);
-  --header-background-color: #eee;
+  --header-background-color: var(--background-color-tertiary);
   --header-border-bottom: 1px solid var(--border-color);
   --header-border-image: '';
   --header-box-shadow: none;
@@ -164,9 +170,13 @@
   --syntax-title-color: #0000c0;
   --syntax-type-color: #2a66d9;
   --syntax-variable-color: var(--primary-text-color);
+
   /* misc */
   --border-radius: 4px;
   --reply-overlay-z-index: 1000;
+
+  /* paper and iron component overrides */
+  --iron-overlay-backdrop-background-color: black;
   --iron-overlay-backdrop-opacity: 0.32;
   --iron-overlay-backdrop: {
     transition: none;
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index 4a91774f..78bc48b 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -30,7 +30,7 @@
       --primary-text-color: #e8eaed;
       --link-color: #8ab4f8;
       --comment-text-color: var(--primary-text-color);
-      --deemphasized-text-color: #9e9e9e;
+      --deemphasized-text-color: #9aa0a6;
       --default-button-text-color: #8ab4f8;
       --error-text-color: red;
       --primary-button-text-color: var(--primary-text-color);
@@ -42,28 +42,24 @@
       --vote-text-color-disliked: #d32f2f;
 
       /* background colors */
+      /* primary background colors */
+      --background-color-primary: #202124;
+      --background-color-secondary: #2f3034;
+      --background-color-tertiary: #3b3d3f;
+      /* directly derived from primary background colors */
+      /*   empty, because inheriting from app-theme is just fine
+      /* unique background colors */
       --assignee-highlight-color: #3a361c;
-      --chip-background-color: #131416;
       --comment-background-color: #0b162b;
       --robot-comment-background-color: #e8f0fe;
-      --default-button-background-color: #3c4043;
-      --dialog-background-color: #131416;
-      --dropdown-background-color: #131416;
       --edit-mode-background-color: #5c0a36;
       --emphasis-color: #383f4a;
-      --expanded-background-color: #26282b;
       --hover-background-color: rgba(161, 194, 250, 0.2);
       --primary-button-background-color: var(--link-color);
       --secondary-button-background-color: var(--primary-text-color);
-      --select-background-color: #3c4043;
       --selection-background-color: rgba(161, 194, 250, 0.1);
-      --shell-command-background-color: #5f5f5f;
-      --shell-command-decoration-background-color: #999;
-      --table-header-background-color: #131416;
-      --table-subheader-background-color: rgba(158, 158, 158, 0.24);
       --tooltip-background-color: #111;
       --unresolved-comment-background-color: #385a9a;
-      --view-background-color: #131416;
       --vote-color-approved: #7fb66b;
       --vote-color-disliked: #bf6874;
       --vote-color-neutral: #597280;
@@ -79,9 +75,9 @@
       /* spacing */
 
       /* header and footer */
-      --footer-background-color: #131416;
+      --footer-background-color: var(--background-color-tertiary);
       --footer-border-top: 1px solid var(--border-color);
-      --header-background-color: #3c4043;
+      --header-background-color: var(--background-color-tertiary);
       --header-border-bottom: 1px solid var(--border-color);
       --header-padding: 0 var(--spacing-l);
       --header-text-color: var(--primary-text-color);
@@ -92,7 +88,7 @@
       --dark-rebased-remove-highlight-color: rgba(255, 139, 6, 0.15);
       --dark-remove-highlight-color: #62110f;
       --diff-blank-background-color: #212121;
-      --diff-context-control-background-color: #131416;
+      --diff-context-control-background-color: #333311;
       --diff-context-control-border-color: var(--border-color);
       --diff-context-control-color: var(--deemphasized-text-color);
       --diff-highlight-range-color: rgba(0, 100, 200, 0.5);
@@ -137,6 +133,9 @@
 
       /* misc */
 
+      /* paper and iron component overrides */
+      --iron-overlay-backdrop-background-color: white;
+
       /* rules applied to <html> */
       background-color: var(--view-background-color);
     }
diff --git a/tools/nongoogle.bzl b/tools/nongoogle.bzl
index 6a29da6..e16c0a0 100644
--- a/tools/nongoogle.bzl
+++ b/tools/nongoogle.bzl
@@ -23,8 +23,8 @@
 
     maven_jar(
         name = "dropwizard-core",
-        artifact = "io.dropwizard.metrics:metrics-core:4.1.1",
-        sha1 = "ebfafc716d9c3b6151dc7c2c09ce925a163a4f21",
+        artifact = "io.dropwizard.metrics:metrics-core:4.1.2",
+        sha1 = "bba231bbf3024c19e75622ec168821cbbd4261a4",
     )
 
     SSHD_VERS = "2.3.0"