SDK / exoplayer

1. AudioDecoderTrackRenderer now reports decoder initialization
   and AudioTrack underruns.
2. AudioDecoderTrackRenderer can now render more than one output
   buffer per call to doSomeWork, to be consistent with
   MediaCodecAudioTrackRenderer. This may also prevent audio
   underruns in the case that audio is fragmented into many small
   buffers.
3. AudioDecoderTrackRenderer now has an overridable method that
   receives the audio session id, to be consistent with
   MediaCodecAudioTrackRenderer.
4. Fix unsafe event notification in LibvpxVideoTrackRenderer.
5. Vpx and AudioDecoder extensions now increment the CodecCounter
   inputBufferCount field correctly.
6. Decoders now have names :).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=122250009