Call center after reply dialog open promise resolves

On domains with plugins (e.g. chromium-review), viewing a diff in a
change before actually viewing the change and then navigating to the
change-view with the 'a' keyboard shortcut can cause the reply dialog
to be improperly placed on the page.

With this change, `_openReplyDialog` centers the dialog after it's
opened.

Bug: Issue 5506
Change-Id: Id72d428be8e6d8492a2c6d90be372163fad7b82d

polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js

@@ -528,7 +528,6 @@
 
         if (this.viewState.showReplyDialog) {
           this._openReplyDialog();
-          this.async(function() { this.$.replyOverlay.center(); }, 1);
           this.set('viewState.showReplyDialog', false);
         }
       }.bind(this));
@@ -542,7 +541,7 @@
         // another, so that the user's preference is restored.
         this.set('viewState.diffMode', null);
         this.set('_numFilesShown', DEFAULT_NUM_FILES_SHOWN);
-     }
+      }
       this.set('viewState.changeNum', this._changeNum);
       this.set('viewState.patchRange', this._patchRange);
     },
@@ -838,6 +837,8 @@
       this.$.replyOverlay.open().then(function() {
         this.$.replyOverlay.setFocusStops(this.$.replyDialog.getFocusStops());
         this.$.replyDialog.open(opt_section);
+        Polymer.dom.flush();
+        this.$.replyOverlay.center();
       }.bind(this));
     },