resolve merge conflicts of 823bd74 to lmp-mr1-dev am: 67ca3caf10 am: 6b52fd6b67
am: f4285f22bf

* commit 'f4285f22bfe47791a1d21eaa28a4afce23f47c8d':
  MPEG4Extractor: ensure kKeyTrackID exists before creating an MPEG4Source as track.

Change-Id: I71b691a769641d3e3137b4fd954d784d073b9074