Make it clear that non-optional MediaFormat keys are required
Make it clear that non-optional MediaFormat keys are required

Also mark KEY_CHANNEL_MASK optional.

Change-Id: I569087f564dc60a89b15a3440a9b1c538927f610

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