Properly center the reply dialog when coming from the diff view

Previously it was not centered when pressing the 'a' shortcut
from within the diff view.

Change-Id: I2f685b0345065f5b1d599b973eb0750b3d9cb925
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 bc57dd9..831fdb8 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
@@ -283,6 +283,7 @@
 
         if (this.viewState.showReplyDialog) {
           this.$.replyOverlay.open();
+          this.async(function() { this.$.replyOverlay.center(); }, 1);
           this.set('viewState.showReplyDialog', false);
         }
       }.bind(this));