MediaSessionCompat: Set default callback to pass extra binder

This CL sets default callback in MediaSessionCompat's constructor to respond
to the MediaControllerCompat's request for the extra binder.

Bug: 32129662
Test: Tested sendSessionEvent() with Support4Demos on API 21 and 22
Change-Id: Iafe894136b23a0ae3d5e8a0368c0827abd1dffe7
1 file changed