Revert of Update AudioRenderer API to fire changes in BufferingState (round 2). ...

Revert of Update AudioRenderer API to fire changes in BufferingState (round 2). (https://codereview.chromium.org/354673007/)

Reason for revert:
This CL broke PipelineIntegrationTest.* tests under memory tools: crbug.com/389104

Original issue's description:
> Update AudioRenderer API to fire changes in BufferingState (round 2).
>
> As a result, Pipeline now handles prerolling and underflow/rebuffering
> by listening for BUFFERING_HAVE_NOTHING/ENOUGH callbacks. Preroll() is
> renamed StartPlayingFrom() and no longer accepts a completion callback.
> In this new model, AudioRenderers immediately enter and remain in
> the "playing" state and fire buffering state callbacks to let Pipeline
> know when to start/stop the clock.
>
> BUG=144683
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=279977

TBR=xhwang@chromium.org,scherkus@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=144683

Review URL: https://codereview.chromium.org/357953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@279990 0039d316-1c4b-4281-b951-d872f2087c98