resolve merge conflicts of 823bd74 to lmp-mr1-dev am: 67ca3caf10 am: 6b52fd6b67 am: f4285f22bf
am: 87406db29c

* commit '87406db29c09e16df8f0d82dd0547d3fb953ab92':
  MPEG4Extractor: ensure kKeyTrackID exists before creating an MPEG4Source as track.

Change-Id: I6f37992a285efbc2fa08da3b0f6e6f0fecb52b07