- Also refactor decryptor management code out of mp4_media_parser.cc
- Move decryptor managment logic to DecryptorSource class to make it
available for webm as well
- Remove data_offset member from DecryptConfig which is not useful
- Add widevine_pssh_data.proto file
Closes#72
Change-Id: I1d32baf4013ebd3382b5372c7433fae5033a260e