Merge "DO NOT MERGE - MPEG4Extractor: Check mLastTrack before dereferencing." into lmp-dev am: b6ba3d7e47  -s ours am: 37e3ea354a am: ea136eb981  -s ours am: 2456e12801 am: fe97b39795 am: 3c76391550 am: 1099791bd6  -s ours am: 0e4feca95e
am: 9356956742

Change-Id: Ic101bafbd673bb5ded913a72718b0cb982533241