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This is part of the work to rewire the audio playback logic for iOS
(and potentially also for Android).

AudioJitterBuffer acts as a jitter buffer that queues up AudioPackets
once they are received and before they are consumed by a native playback
queue.
This class is basically modified from AudioPlayerBuffer with a few
changes:
* Allow handling packets in different stream formats/sample rate and
  call a callback when the format is changed.
* Move the underrun protection logic from AudioPlayerIos (the
  "PRIMING" state) into the jitter buffer.
* Fix a bug where bytes_extracted_ is ignored when copying audio data.
* Removed the AudioStreamConsumer inheritance, Stop() and other unused
  logic.

Bug: 868088
Change-Id: Ibaee655df28de68f5303d735ef89cf15695ab2ff
Reviewed-on: https://chromium-review.googlesource.com/1150936
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580709}