Whenever a comment changes in either the thread view or the diff view,
the other view will need to be notified of the change in order to
re-render its comments, since they do not share a common data source
(The diff view's comments are added manually when the diff is rendered
via the diff builder).
Because the gr-diff-comment-thread is common to both uses, it can fire
events to be consumed in both cases.
From there, gr-diff and gr-list-view each fire a separate event, which
is listened for on the change view (common ancestor). The change view
will then trigger reloading of comments for the element that needs
Change-Id: Ia31c0ef512af408c4d099667558a32f86ed43152
e115b14541