resolve merge conflicts of 823bd74 to lmp-mr1-dev am: 67ca3caf10 am: 6b52fd6b67 am: f4285f22bf am: 87406db29c
am: 5f44938fe9

* commit '5f44938fe991e19dd694a08c5e8911a9ffa2670b':
  MPEG4Extractor: ensure kKeyTrackID exists before creating an MPEG4Source as track.

Change-Id: I961243ce29ba0296ad9aad927424cc67b39489e3