Add Brightness setting for VR Mode.

This change saves and loads a different brightness setting when the user
goes in and out of VR Mode.

Bug: 30984614
Merged-In: Ie5578bbd6ea346f0eb34fe4abbfd604a5d7c0c93
Change-Id: Ie5578bbd6ea346f0eb34fe4abbfd604a5d7c0c93
14 files changed