Media controller now fades between different states. The code for
doing this was already there, but this CL enables them and changes
the behavior of transition's OnPreDrawListener to do the right thing.
Also, this CL fixes a bug in ChangeText found while testing this change.
Issue #11083563 ChangeText transition crashes when KEEP transition type used
Change-Id: I5e04c28e1b5faac017b0a4e49734d9faa7fe79cd
aa00613322