Don't update subject in onUserVisibleHintChanged

1. Changing the subject in onUserVisibleHintChanged is overkill. The
   actionbar subject is changed by the controller, and the
   conversation view subject should be changed as a result of
   updates to the current conversation.

2. Only perform the operations in onUserVisibleHintChanged if the
   fragment is visible to the user.

Bug: 8025544 Call to setSubject in
             ConversationViewFragment.onLoadFinished

Change-Id: I71bd78641f20635709bc1dafb5c37942c249effe
3 files changed