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The name content::VideoFrameProvider was easy to cause confusion with
cc:VideoFrameProvider. Furthermore, the methods provided in the
content::VideoFrameProvider are not specific to Video, which makes the
name somewhat unsuitable.

List of changes:
* Moved the typedef content::VideoFrameProvider::RepaintCB out to a new
  file and renamed it to VideoFrameCallback.
* Renamed interface VideoFrameProvider to PausableStream
* Renamed method Play() to Resume()

BUG=526835

Review-Url: https://codereview.chromium.org/2005053006
Cr-Commit-Position: refs/heads/master@{#398071}