Fixing a condition that can cause deadlock

Callbacks on ServiceConnection happen on the main UI thread for an
application. Since the thread that calls bindService then immediately
blocks to wait for the service to be connected, this will cause a
deadlock if key operations are happening on the main UI thread.

This bug has likely not been detected yet since key operations are not
supposed to be performed on the main UI thread, however it was uncovered
in a similar application during other testing. This fix ensures the
ServiceConnection object's callbacks will be triggered from a separate
thread from the calling thread.

Bug: 196571032
Test: Apps that run key operations on the UI thread don't hang.
Change-Id: I630a0ef2560a8ebd962de54c65e3d6277133a1cb
Merged-In: I630a0ef2560a8ebd962de54c65e3d6277133a1cb