Fix local storage with PARENT revision

Previously, if a PARENT revision was getting compared to a patchset,
the local storage key would be the same for both, and there were issues
if a user was trying to write drafts on the same line on either side.

This addresses the issue by storing 'PARENT' as the patch number in the
local storage key, so that each key is unique.

Bug: Issue 5412
Change-Id: Ia8b2f0abe1d24a3849628fe335c931f07bcaff52

polygerrit-ui/app/elements/diff/gr-diff-comment-thread/gr-diff-comment-thread.html

@@ -59,6 +59,7 @@ limitations under the License.
             draft="[[comment.__draft]]"
             show-actions="[[_showActions]]"
             comment-side="[[comment.__commentSide]]"
+            side="[[side]]"
             project-config="[[projectConfig]]"
             on-create-fix-comment="_handleCommentFix"
             on-comment-discard="_handleCommentDiscard"></gr-diff-comment>

polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment.js

@@ -170,7 +170,7 @@
     _eraseDraftComment: function() {
       this.$.storage.eraseDraftComment({
         changeNum: this.changeNum,
-        patchNum: this.patchNum,
+        patchNum: this._getPatchNum(),
         path: this.comment.path,
         line: this.comment.line,
         range: this.comment.range,
@@ -288,7 +288,7 @@
 
         var commentLocation = {
           changeNum: this.changeNum,
-          patchNum: this.patchNum,
+          patchNum: this._getPatchNum(),
           path: this.comment.path,
           line: this.comment.line,
           range: this.comment.range,
@@ -410,6 +410,10 @@
           draft);
     },
 
+    _getPatchNum: function() {
+      return this.side === 'PARENT' ? 'PARENT' : this.patchNum;
+    },
+
     _loadLocalDraft: function(changeNum, patchNum, comment) {
       // Only apply local drafts to comments that haven't been saved
       // remotely, and haven't been given a default message already.
@@ -423,7 +427,7 @@
 
       var draft = this.$.storage.getDraftComment({
         changeNum: changeNum,
-        patchNum: patchNum,
+        patchNum: this._getPatchNum(),
         path: comment.path,
         line: comment.line,
         range: comment.range,

polygerrit-ui/app/elements/diff/gr-diff-comment/gr-diff-comment_test.html

@@ -152,6 +152,14 @@ limitations under the License.
       });
     });
 
+    test('_getPatchNum', function() {
+      element.side = 'PARENT';
+      element.patchNum = 1;
+      assert.equal(element._getPatchNum(), 'PARENT');
+      element.side = 'REVISION';
+      assert.equal(element._getPatchNum(), 1);
+    });
+
     test('comment expand and collapse', function() {
       element.collapsed = true;
       assert.isFalse(isVisible(element.$$('gr-formatted-text')),