SDK / exoplayer

- Rename preparePlayer to initializePlayer, to reflect the fact that the
preparing state is gone. Replace playerNeedsPrepare with playerNeedsSource.
- playWhenReady is now always true in calls to initializePlayer.
- Handle the intent just before setting the source.
- Use URIs consistently instead of Strings to avoid reparsing.
- onShown becomes initializePlayer.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120125576