In this CL:
* PesReader moves out of TsExtractor and becomes public.
* ElementaryStreamReaderFactory becomes TsPayloadReaderFactory and is
moved to TsPayloadReader.
* The TsPayloadReaderFactory is in charge of wrapping any
ElementaryStreamReaders with a PesReader.
Incoming:
* Extract SectionReader supperclass (analog to PesReader, but for
sections) from Pat and Pmt readers.
* Add a ScteReader, wrapped by a section reader, and include it in
the DefaultTsPayloadReaderFactory.
Issue:#726
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=136707706
