Use 'Commit message' and 'Merge list' in comment-list

This brings the comment list (both in the messages at the bottom
and in the reply modal dialog) into line with the file list,
emails, and other places the file names are displayed.

Change-Id: Id0ef2e3bafb63070d2284e4b70613ac92300d14d
(cherry picked from commit b82043a3a5)

polygerrit-ui/app/elements/change/gr-comment-list/gr-comment-list.html

@@ -48,7 +48,9 @@ limitations under the License.
     </style>
     <template is="dom-repeat" items="[[_computeFilesFromComments(comments)]]" as="file">
       <div class="file">
-        <a href$="[[_computeFileDiffURL(file, changeNum, patchNum)]]">[[file]]</a>:
+        <a href$="[[_computeFileDiffURL(file, changeNum, patchNum)]]">
+          [[_computeFileDisplayName(file)]]
+        </a>:
       </div>
       <template is="dom-repeat"
                 items="[[_computeCommentsForFile(comments, file)]]" as="comment">

polygerrit-ui/app/elements/change/gr-comment-list/gr-comment-list.js

@@ -14,6 +14,9 @@
 (function() {
   'use strict';
 
+  var COMMIT_MESSAGE_PATH = '/COMMIT_MSG';
+  var MERGE_LIST_PATH = '/MERGE_LIST';
+
   Polymer({
     is: 'gr-comment-list',
 
@@ -39,6 +42,15 @@
         '/' + patchNum + '/' + file;
     },
 
+    _computeFileDisplayName: function(path) {
+      if (path === COMMIT_MESSAGE_PATH) {
+        return 'Commit message';
+      } else if (path === MERGE_LIST_PATH) {
+        return 'Merge list';
+      }
+      return path;
+    },
+
     _isOnParent: function(comment) {
       return comment.side === 'PARENT';
     },

polygerrit-ui/app/elements/change/gr-comment-list/gr-comment-list_test.html

@@ -65,6 +65,15 @@ limitations under the License.
       assert.equal(actual, expected);
     });
 
+    test('_computeFileDisplayName', function() {
+      assert.equal(element._computeFileDisplayName('/COMMIT_MSG'),
+          'Commit message');
+      assert.equal(element._computeFileDisplayName('/MERGE_LIST'),
+          'Merge list');
+      assert.equal(element._computeFileDisplayName('/foo/bar/baz'),
+          '/foo/bar/baz');
+    });
+
     test('_computeDiffLineURL', function() {
       var comment = {line: 123, side: 'REVISION', patch_set: 10};
       var expected = '/c/<change>/<patch>/<file>#123';