AnnounceForAccessibility is broken for any view that has a ContentDescription.

1. The purpose of the View#announceForAccessibility method is to
   give a message to the user that is not related to a predefined
   view state change. The current implementation is grabbing the
   source view's content description which in general overrides
   the event text which defeats the purpose of the announcement.

bug:6721440

Change-Id: I8814914bea38c5f4c04f57391a64cf2bb06cb975