MediaSessionCompat: Remove looper requirement in constructor

Instead of requiring the constructor of MediaSessionCompat to be
called on a thread with a looper, mirror the behavior in
MediaSession and only require a looper thread when setCallback() is
called and drop all callbacks until that point.

BUG: 25079496
Change-Id: I42b11777d635d5d5df7ccb02e92fbf28c189c806
1 file changed