SDK / exoplayer

- Remove special DefaultTrackOutput.sampleData method, and have
  SingleSampleMediaChunk use the regular one instead.
- Make DummyTrackOutput behave correctly is allowEndOfInput is
  false.
- Simplify progress tracking in ExtractorSampleSource.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117808659