1. The need for sending an accessibility event to announce a context change
which does not cleanly fit into the existing UI transition UI events has
come quite a few time in application development. To avoid retrofitting
accessibility event types that do not semantically match the intent to
just announce a short message this patch is adding specialized event type.
Also a helper method on View is added to sheild developers from knowing
how to construct and send such an event.
bug:5977979
Change-Id: Iaf5f620426f8616be67fbf243a02ad5b606c949b
51ab90cab1