SDK / exoplayer

- HlsDownloader.loadManifest (previously called getHlsPlaylist)
  suppressed errors for the offline case, where-as the DashUtil
  equivalent method did not. This change makes them consistent
  and moves both other to use ParsingLoadable.
- Enable GZIP for manifest loads in both cases.
- Use Uri rather than String to represent Uris. Previously the
  strings were parsed into Uris quite deep in the code, which
  isn't ideal if the parsing fails; you'd probably prefer the
  error to occur early at the top level.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=165181398