Merge changes Icd6d4fc4,Idff221fc,I99f0f79a,Ic310f937,I74879023, ...

* changes:
  stagefright: rework MediaCodecSource
  stagefright/rtsp: Remove dependence on OMXSource
  cmds/stagefright: use MediaCodec* instead of OMXCodec
  stagefright: add SimpleDecodingSource
  stagefright/foundation: add Mutexed syntactic sugar
  stagefright: add PREFER_SOFTWARE_CODEC flag to MediaCodecSource
  stagefright: move MetadataRetriever off of OMXCodec
  stagefright: change signature of MediaCodec::Create methods
  stagefright: create findCodec methods in MediaCodecList
  stagefright: move getOMXChannelMapping to ACodec
  stagefright: Remove unused ClockEstimator and TimeSource
  stagefright: Remove unused TimedTextDriver and Sources