SDK / exoplayer

- Make sure no events are posted on PlaybackControlView
  if it's not attached to a window. This can cause leaks.
  The target hide time is recorded if necessary and
  processed when the view is re-attached.
- Deduplicated PlaybackControlView.VisibilityListener
  invocations.
- Fixed timeouts to be more intuitive (I think).
- Fixed initial visibility of PlaybackControlView when
  used as part of SimpleExoPlayerView.
- Made some more attributes configurable from layout xml.

Issue: #1908
Issue: #1919
Issue: #1923

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135679988