Bug 5080320 MediaPlayer volume
Glenn Kasten authored
Details:
 - re-factor volume-related code yet again
 - remove dead variables mAmplFromVolLevel, mAmplFromStereoPos, mDirectLevel
 - add placeholders for kEventPrefetchFillLevelUpdate and kEventPrefetchStatusChange

Known issues:
 - MPEG-2 TS doesn't yet implement the ability to query channel count, so default to stereo

Change-Id: Ic0f2297b267dc3d380755e8d314e1d5f0f659d7c
99b92775