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 1ab8a77..553e1dd 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
@@ -18,6 +18,7 @@
 <link rel="import" href="../../../behaviors/gr-patch-set-behavior/gr-patch-set-behavior.html">
 <link rel="import" href="../../../behaviors/gr-url-encoding-behavior.html">
 <link rel="import" href="../../../bower_components/polymer/polymer.html">
+<link rel="import" href="../../core/gr-reporting/gr-reporting.html">
 <link rel="import" href="../../diff/gr-diff/gr-diff.html">
 <link rel="import" href="../../diff/gr-diff-cursor/gr-diff-cursor.html">
 <link rel="import" href="../../shared/gr-button/gr-button.html">
@@ -243,7 +244,7 @@
             aria-label$="[[_computeFileStatusLabel(file.status)]]">
           [[_computeFileStatus(file.status)]]
         </div>
-        <a class$="[[_computePathClass(file.__expanded)]]"
+        <a class$="[[_computePathClass(file.__path, _expandedFilePaths.*)]]"
             href$="[[_computeDiffURL(changeNum, patchRange, file.__path)]]"
             on-click="_handleFileClick">
           <div title$="[[_computeFileDisplayName(file.__path)]]"
@@ -297,15 +298,16 @@
         <div class="show-hide" hidden$="[[_userPrefs.expand_inline_diffs]]">
           <label class="show-hide">
             <input type="checkbox" class="show-hide"
-                checked$="[[!file.__expanded]]" data-path$="[[file.__path]]"
+                checked$="[[_isFileExpanded(file.__path, _expandedFilePaths.*)]]"
+                data-path$="[[file.__path]]"
                 on-change="_handleHiddenChange">
-            [[_computeShowHideText(file.__expanded)]]
+            [[_computeShowHideText(file.__path, _expandedFilePaths.*)]]
           </label>
         </div>
       </div>
       <gr-diff
-          hidden$="[[!file.__expanded]]"
-          expanded="[[file.__expanded]]"
+          no-auto-render
+          hidden$="[[!_isFileExpanded(file.__path, _expandedFilePaths.*)]]"
           project="[[change.project]]"
           commit="[[change.current_revision]]"
           change-num="[[changeNum]]"
@@ -366,6 +368,7 @@
         id="fileCursor"
         scroll-behavior="keep-visible"
         cursor-target-class="selected"></gr-cursor-manager>
+    <gr-reporting id="reporting"></gr-reporting>
   </template>
   <script src="gr-file-list.js"></script>
 </dom-module>
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 8016f98..a4992df 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
@@ -104,6 +104,10 @@
         readOnly: true,
         value: 50,
       },
+      _expandedFilePaths: {
+        type: Array,
+        value: function() { return []; },
+      },
     },
 
     behaviors: [
@@ -112,6 +116,10 @@
       Gerrit.URLEncodingBehavior,
     ],
 
+    observers: [
+      '_expandedPathsChanged(_expandedFilePaths.splices)',
+    ],
+
     keyBindings: {
       'shift+left': '_handleShiftLeftKey',
       'shift+right': '_handleShiftRightKey',
@@ -218,8 +226,18 @@
     },
 
     _handleHiddenChange: function(e) {
-      var model = e.model;
-      model.set('file.__expanded', !model.file.__expanded);
+      this._togglePathExpanded(e.model.file.__path);
+    },
+
+    _togglePathExpanded: function(path) {
+      // Is the path in the list of expanded diffs? IF so remove it, otherwise
+      // add it to the list.
+      var pathIndex = this._expandedFilePaths.indexOf(path);
+      if (pathIndex === -1) {
+        this.push('_expandedFilePaths', path);
+      } else {
+        this.splice('_expandedFilePaths', pathIndex, 1);
+      }
     },
 
     _handlePatchChange: function(e) {
@@ -236,25 +254,26 @@
       }
     },
 
-    /**
-     * Until upgrading to Polymer 2.0, manual management of reflection between
-     * _shownFiles and _files is necessary. Performance of linkPaths is very
-     * poor.
-     */
     _expandAllDiffs: function(e) {
       this._showInlineDiffs = true;
+
+      // Find the list of paths that are in the file list, but not in the
+      // expanded list.
+      var newPaths = [];
+      var path;
       for (var i = 0; i < this._shownFiles.length; i++) {
-        this.set(['_shownFiles', i, '__expanded'], true);
-        this.set(['_files', i, '__expanded'], true);
+        path = this._shownFiles[i].__path;
+        if (this._expandedFilePaths.indexOf(path) === -1) {
+          newPaths.push(path);
+        }
       }
+
+      this.splice.apply(this, ['_expandedFilePaths', 0, 0].concat(newPaths));
     },
 
     _collapseAllDiffs: function(e) {
       this._showInlineDiffs = false;
-      for (var i = 0; i < this._shownFiles.length; i++) {
-        this.set(['_shownFiles', i, '__expanded'], false);
-        this.set(['_files', i, '__expanded'], false);
-      }
+      this._expandedFilePaths = [];
       this.$.diffCursor.handleDiffUpdate();
     },
 
@@ -328,7 +347,6 @@
           this.changeNum, this.patchRange).then(function(files) {
             // Append UI-specific properties.
             return files.map(function(file) {
-              file.__expanded = false;
               return file;
             });
           });
@@ -365,12 +383,7 @@
           this.$.fileCursor.index === -1) { return; }
 
       e.preventDefault();
-      var expanded = this._files[this.$.fileCursor.index].__expanded;
-      // Until Polymer 2.0, manual management of reflection between _files
-      // and _shownFiles is necessary.
-      this.set(['_shownFiles', this.$.fileCursor.index, '__expanded'],
-          !expanded);
-      this.set(['_files', this.$.fileCursor.index, '__expanded'], !expanded);
+      this._togglePathExpanded(this.$.fileCursor.target.path);
     },
 
     _handleCapitalIKey: function(e) {
@@ -573,12 +586,13 @@
       return classes.join(' ');
     },
 
-    _computePathClass: function(expanded) {
-      return expanded ? 'path expanded' : 'path';
+    _computePathClass: function(path, expandedFilesRecord) {
+      return this._isFileExpanded(path, expandedFilesRecord) ? 'path expanded' :
+          'path';
     },
 
-    _computeShowHideText: function(expanded) {
-      return expanded ? '▼' : '◀';
+    _computeShowHideText: function(path, expandedFilesRecord) {
+      return this._isFileExpanded(path, expandedFilesRecord) ? '▼' : '◀';
     },
 
     _computeFilesShown: function(numFilesShown, files) {
@@ -663,5 +677,74 @@
       return FileStatus.hasOwnProperty(statusCode) ?
           FileStatus[statusCode] : 'Status Unknown';
     },
+
+    _isFileExpanded: function(path, expandedFilesRecord) {
+      return expandedFilesRecord.base.indexOf(path) !== -1;
+    },
+
+    /**
+     * Handle splices to the list of expanded file paths. If there are any new
+     * entries in the expanded list, then render each diff corresponding in
+     * order by waiting for the previous diff to finish before starting the next
+     * one.
+     * @param  {splice} record The splice record in the expanded paths list.
+     */
+    _expandedPathsChanged: function(record) {
+      if (!record) { return; }
+
+      // Find the paths introduced by the new index splices:
+      var newPaths = record.indexSplices
+          .map(function(splice) {
+            return splice.object.slice(splice.index,
+                splice.index + splice.addedCount);
+          })
+          .reduce(function(acc, paths) { return acc.concat(paths); }, []);
+
+      var timerName = 'Expand ' + newPaths.length + ' diffs';
+      this.$.reporting.time(timerName);
+
+      this._renderInOrder(newPaths, this.diffs, newPaths.length)
+          .then(function() {
+            this.$.reporting.timeEnd(timerName);
+            this.$.diffCursor.handleDiffUpdate();
+          }.bind(this));
+    },
+
+    /**
+     * Given an array of paths and a NodeList of diff elements, render the diff
+     * for each path in order, awaiting the previous render to complete before
+     * continung.
+     * @param  {!Array<!String>} paths
+     * @param  {!NodeList<!GrDiffElement>} diffElements
+     * @param  {Number} initialCount The total number of paths in the pass. This
+     *   is used to generate log messages.
+     * @return {!Promise}
+     */
+    _renderInOrder: function(paths, diffElements, initialCount) {
+      if (!paths.length) {
+        console.log('Finished expanding', initialCount, 'diff(s)');
+        return Promise.resolve();
+      }
+      console.log('Expanding diff', 1 + initialCount - paths.length, 'of',
+          initialCount, ':', paths[0]);
+      var diffElem = this._findDiffByPath(paths[0], diffElements);
+      return diffElem.reload().then(function() {
+        return this._renderInOrder(paths.slice(1), diffElements, initialCount);
+      }.bind(this));
+    },
+
+    /**
+     * In the given NodeList of diff elements, find the diff for the given path.
+     * @param  {!String} path
+     * @param  {!NodeList<!GrDiffElement>} diffElements
+     * @return {!GrDiffElement}
+     */
+    _findDiffByPath: function(path, diffElements) {
+      for (var i = 0; i < diffElements.length; i++) {
+        if (diffElements[i].path === path) {
+          return diffElements[i];
+        }
+      }
+    },
   });
 })();
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.html b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.html
index 4c8b4f1..1fb9b60 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.html
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.html
@@ -80,19 +80,16 @@
           lines_inserted: 9,
           lines_deleted: 0,
           __path: '/COMMIT_MSG',
-          __expanded: false,
         });
         assert.deepEqual(files[1], {
           lines_inserted: 0,
           lines_deleted: 0,
           __path: 'about.txt',
-          __expanded: false,
         });
         assert.deepEqual(files[2], {
           lines_inserted: 0,
           lines_deleted: 123,
           __path: 'tags.html',
-          __expanded: false,
         });
 
         getChangeFilesStub.restore();
@@ -270,9 +267,9 @@
     suite('keyboard shortcuts', function() {
       setup(function() {
         element._files = [
-          {__path: '/COMMIT_MSG', __expanded: false},
-          {__path: 'file_added_in_rev2.txt', __expanded: false},
-          {__path: 'myfile.txt', __expanded: false},
+          {__path: '/COMMIT_MSG'},
+          {__path: 'file_added_in_rev2.txt'},
+          {__path: 'myfile.txt'},
         ];
         element.changeNum = '42';
         element.patchRange = {
@@ -333,29 +330,31 @@
       });
 
       test('i key shows/hides selected inline diff', function() {
+        sandbox.stub(element, '_expandedPathsChanged');
         flushAsynchronousOperations();
         element.$.fileCursor.stops = element.diffs;
         element.$.fileCursor.setCursorAtIndex(0);
         MockInteractions.pressAndReleaseKeyOn(element, 73, null, 'i');
         flushAsynchronousOperations();
-        assert.isFalse(element.diffs[0].hasAttribute('hidden'));
+        assert.include(element._expandedFilePaths, element.diffs[0].path);
         MockInteractions.pressAndReleaseKeyOn(element, 73, null, 'i');
         flushAsynchronousOperations();
-        assert.isTrue(element.diffs[0].hasAttribute('hidden'));
+        assert.notInclude(element._expandedFilePaths, element.diffs[0].path);
         element.$.fileCursor.setCursorAtIndex(1);
         MockInteractions.pressAndReleaseKeyOn(element, 73, null, 'i');
         flushAsynchronousOperations();
-        assert.isFalse(element.diffs[1].hasAttribute('hidden'));
+        assert.include(element._expandedFilePaths, element.diffs[1].path);
 
         MockInteractions.pressAndReleaseKeyOn(element, 73, 'shift', 'i');
         flushAsynchronousOperations();
         for (var index in element.diffs) {
-          assert.isFalse(element.diffs[index].hasAttribute('hidden'));
+          assert.include(element._expandedFilePaths, element.diffs[index].path);
         }
         MockInteractions.pressAndReleaseKeyOn(element, 73, 'shift', 'i');
         flushAsynchronousOperations();
         for (var index in element.diffs) {
-          assert.isTrue(element.diffs[index].hasAttribute('hidden'));
+          assert.notInclude(element._expandedFilePaths,
+              element.diffs[index].path);
         }
       });
     });
@@ -440,9 +439,9 @@
 
     test('file review status', function() {
       element._files = [
-        {__path: '/COMMIT_MSG', __expanded: false},
-        {__path: 'file_added_in_rev2.txt', __expanded: false},
-        {__path: 'myfile.txt', __expanded: false},
+        {__path: '/COMMIT_MSG'},
+        {__path: 'file_added_in_rev2.txt'},
+        {__path: 'myfile.txt'},
       ];
       element._reviewed = ['/COMMIT_MSG', 'myfile.txt'];
       element.changeNum = '42';
@@ -537,7 +536,7 @@
 
     test('checkbox shows/hides diff inline', function() {
       element._files = [
-        {__path: 'myfile.txt', __expanded: false},
+        {__path: 'myfile.txt'},
       ];
       element.changeNum = '42';
       element.patchRange = {
@@ -545,14 +544,16 @@
         patchNum: '2',
       };
       element.$.fileCursor.setCursorAtIndex(0);
+      sandbox.stub(element, '_expandedPathsChanged');
       flushAsynchronousOperations();
       var fileRows =
           Polymer.dom(element.root).querySelectorAll('.row:not(.header)');
       var showHideCheck = fileRows[0].querySelector(
           'input.show-hide[type="checkbox"]');
-      assert.isTrue(showHideCheck.checked);
+      assert.isNotOk(showHideCheck.checked);
       MockInteractions.tap(showHideCheck);
-      assert.isFalse(element.diffs[0].hidden);
+      assert.isOk(showHideCheck.checked);
+      assert.notEqual(element._expandedFilePaths.indexOf('myfile.txt'), -1);
     });
 
     test('path should be properly escaped', function() {
@@ -575,7 +576,7 @@
 
     test('diff mode correctly toggles the diffs', function() {
       element._files = [
-        {__path: 'myfile.txt', __expanded: false},
+        {__path: 'myfile.txt'},
       ];
       element.changeNum = '42';
       element.patchRange = {
@@ -628,7 +629,7 @@
         assert.isTrue(computeSpy.lastCall.returnValue);
         var arr = [];
         _.times(element._maxFilesForBulkActions + 1, function() {
-          arr.push({__path: 'myfile.txt', __expanded: false});
+          arr.push({__path: 'myfile.txt'});
         });
         element._files = arr;
         element._numFilesShown = arr.length;
@@ -639,7 +640,7 @@
 
     test('expanded attribute not set on path when not expanded', function() {
       element._files = [
-        {__path: '/COMMIT_MSG', __expanded: false},
+        {__path: '/COMMIT_MSG'},
       ];
       assert.isNotOk(element.$$('.expanded'));
     });
@@ -659,13 +660,14 @@
     });
     test('expand_inline_diffs user preference', function() {
       element._files = [
-        {__path: '/COMMIT_MSG', __expanded: false},
+        {__path: '/COMMIT_MSG'},
       ];
       element.changeNum = '42';
       element.patchRange = {
         basePatchNum: 'PARENT',
         patchNum: '2',
       };
+      sandbox.stub(element, '_expandedPathsChanged');
       flushAsynchronousOperations();
       var commitMsgFile = Polymer.dom(element.root)
           .querySelectorAll('.row:not(.header) a')[0];
@@ -686,5 +688,59 @@
       assert(hiddenChangeSpy.calledOnce, 'file is expanded');
       assert.isOk(element.$$('.expanded'));
     });
+
+    test('_togglePathExpanded', function() {
+      var path = 'path/to/my/file.txt';
+      element.files = [{__path: path}];
+      var expandedChangedStub = sandbox.stub(element, '_expandedPathsChanged');
+
+      assert.equal(element._expandedFilePaths.length, 0);
+      element._togglePathExpanded(path);
+      assert.equal(expandedChangedStub.callCount, 1);
+      assert.include(element._expandedFilePaths, path);
+      element._togglePathExpanded(path);
+      assert.equal(expandedChangedStub.callCount, 2);
+      assert.notInclude(element._expandedFilePaths, path);
+    });
+
+    test('_expandedPathsChanged', function(done) {
+      var path = 'path/to/my/file.txt';
+      var diffs = [{
+        path: path,
+        reload: function() {
+          done();
+          return Promise.resolve();
+        },
+      }];
+      var diffsStub = sinon.stub(element, 'diffs', {
+        get: function() { return diffs; },
+      });
+      element.push('_expandedFilePaths', path);
+    });
+
+    test('_renderInOrder', function(done) {
+      var callCount = 0;
+      var diffs = [{
+        path: 'p0',
+        reload: function() {
+          assert.equal(callCount++, 2);
+          return Promise.resolve();
+        },
+      }, {
+        path: 'p1',
+        reload: function() {
+          assert.equal(callCount++, 1);
+          return Promise.resolve();
+        },
+      }, {
+        path: 'p2',
+        reload: function() {
+          assert.equal(callCount++, 0);
+          return Promise.resolve();
+        },
+      }];
+      element._renderInOrder(['p2', 'p1', 'p0'], diffs, 3)
+        .then(function() { done(); });
+    });
   });
 </script>
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
index 9c03d23..8631af7 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder.html
@@ -149,11 +149,11 @@
 
             reporting.timeEnd(TimingLabel.CONTENT);
             reporting.time(TimingLabel.SYNTAX);
-            this.$.syntaxLayer.process().then(function() {
+            return this.$.syntaxLayer.process().then(function() {
               reporting.timeEnd(TimingLabel.SYNTAX);
               reporting.timeEnd(TimingLabel.TOTAL);
-            });
-            this.fire('render');
+              this.fire('render');
+            }.bind(this));
           }.bind(this));
         },
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
index 69eb000..697845e 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js
@@ -34,10 +34,9 @@
 
     properties: {
       changeNum: String,
-      expanded: {
+      noAutoRender: {
         type: Boolean,
-        value: true,
-        observer: '_handleShowDiff',
+        value: false,
       },
       patchRange: Object,
       path: String,
@@ -127,13 +126,14 @@
 
       return Promise.all(promises).then(function() {
         if (this.prefs) {
-          this._render();
+          return this._renderDiffTable();
         }
+        return Promise.resolve();
       }.bind(this));
     },
 
     getCursorStops: function() {
-      if (!this.expanded) {
+      if (this.noAutoRender) {
         return [];
       }
 
@@ -166,14 +166,9 @@
       this.toggleClass('no-left');
     },
 
-    _handleShowDiff: function() {
-      if (this._canRender()) {
-        this.reload();
-      }
-    },
-
     _canRender: function() {
-      return this.changeNum && this.patchRange && this.path && this.expanded;
+      return this.changeNum && this.patchRange && this.path &&
+          !this.noAutoRender;
     },
 
     _getCommentThreads: function() {
@@ -419,12 +414,12 @@
       this.updateStyles();
 
       if (this._diff && this._comments) {
-        this._render();
+        this._renderDiffTable();
       }
     },
 
-    _render: function() {
-      this.$.diffBuilder.render(this._comments, this.prefs);
+    _renderDiffTable: function() {
+      return this.$.diffBuilder.render(this._comments, this.prefs);
     },
 
     _clearDiffContent: function() {
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.html
index 158a9a2..0bbad2c 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_test.html
@@ -572,22 +572,6 @@
           assert.equal(drafts.length, 1);
           assert.equal(drafts[0].id, id);
         });
-
-        test('_handleShowDiff reloads when expanded is made true',
-            function(done) {
-          element.expanded = false;
-          element.changeNum = element._comments.meta.changeNum;
-          element.patchRange = element._comments.meta.patchRange;
-          element.path = element._comments.meta.path;
-
-          var stub = sandbox.stub(element, 'reload', function() {
-            assert.isTrue(stub.called);
-            done();
-          });
-          var spy = sinon.spy(element, '_handleShowDiff');
-          element.set('expanded', true);
-          assert.isTrue(spy.called);
-        });
       });
     });
   });