Revert of Revert of Always post buffering state updates since they may change sink state.

Revert of Revert of Always post buffering state updates since they may change sink state. (patchset #1 id:1 of https://codereview.chromium.org/1159573005/)

Reason for revert:
The original patch was innocent.

Original issue's description:
> Revert of Always post buffering state updates since they may change sink state. (patchset #1 id:1 of https://codereview.chromium.org/1161463006/)
>
> Reason for revert:
> Speculative revert for Blink layout tests crashes on Nexus 4:
> http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Android%20%28Nexus4%29
> (SEGV on CrGpuMain thread is observed)
>
> Sorry if my guess is not correct; there wasn't
> a clear signal to identify the culprit.
>
> Original issue's description:
> > Always post buffering state updates since they may change sink state.
> >
> > The lock must never be held when OnTimeStateChanged() is calling into
> > the VideoRendererSink or we can deadlock the compositor thread.
> >
> > With video-only playback occurs a buffering state change for underflow
> > would immediately invoke OnTimeStateChanged(false) which would try to
> > stop the VideoRendererSink under lock.
> >
> > BUG=496466
> > TEST=video only playback doesn't deadlock.
> >
> > Committed: https://crrev.com/9d8a53f3bf01aed28abbd1f9a713a25362c0d158
> > Cr-Commit-Position: refs/heads/master@{#332772}
>
> TBR=xhwang@chromium.org,dalecurtis@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=496466
>
> Committed: https://crrev.com/9fc2a61ce37405635c5528db9d5773c4f30b592d
> Cr-Commit-Position: refs/heads/master@{#332808}

TBR=xhwang@chromium.org,dalecurtis@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=496466
Committed: https://crrev.com/27d2f647092602ca0c2fd7399ee3bae2ca09dee6
Cr-Commit-Position: refs/heads/master@{#332812}

[Yuta Kitamura, 2015-06-04 10:43:12]

Created Revert of Revert of Always post buffering state updates since they may
change sink state.

[commit-bot: I haz the power, 2015-06-04 10:43:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1157573009/1

[commit-bot: I haz the power, 2015-06-04 10:44:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-04 10:45:13]

Patchset 1 (id:??) landed as
https://crrev.com/27d2f647092602ca0c2fd7399ee3bae2ca09dee6
Cr-Commit-Position: refs/heads/master@{#332812}