MediaRouter group volume reporting
MediaRouter group volume reporting

RouteGroups always report back the loudest volume of their component
routes. Maintain this through volume update requests (such as those
reported by volume hard keys) such that each route updates
individually, but the group slider always indicates the loudest value.

Change-Id: I5de4b9048bf55682b6271e9485fe50496a1c97c2

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base