stagefright-plugins: Implement frame dropping and AV sync

stagefright-plugins: Implement frame dropping and AV sync

 * Keep the video from lagging behind the audio by dropping
   frames when we're too far behind.
 * Set options to improve video playback performance
 * It's still a quite terrible experience without hardware decoding,
   but prior to this patch it was possible that the first slow
   frame would be droped by Stagefright and the lag would just grow,
   resulting in a black screen.

Change-Id: Ib10933d385d593d8e887bca033f22b68a812bc7c