Integrate custom close action in ApiDemos for PiP

The demo Activity simply finishes itself when it receives the callback
from the close action PendingIntent.

Video: http://recall/-/aaaaaabFQoRHlzixHdtY/fR0hxeorlYrxXyzfZ02btK
Bug: 223896879
Test: see video
Change-Id: I94797b666fbcd630c828463668d9bc4e07274cd8
3 files changed