Release focus when gamepad "back" is pressed.
Release focus when gamepad "back" is pressed.

Tested:
Verified that pressing back releases the current focus on ATV "Molly".

Bug: 25863276
Change-Id: If4e5eb9f4a7fd2dcfea2c5d104424255e2a18953

google/flatui,google/flatui,google/flatui,google/flatui