Revert of Remove threading from RendererGpuVideoAcceleratorFactories (https://codereview.chromium.org/
27420004/)
Reason for revert:
Sorry, it looks like you broke the Win 7 Tests (dbg)(2) bot. http://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%282%29/builds/19785
Original issue's description:
> This change removes all the threading considerations from
> GpuVideoAcceleratorFactories (and its implementation,
> RendererGpuVideoAcceleratorFactories). Most notably, it removes Abort() and
> associated functions and state. And with the removal of Abort() and friends,
> we can also remove its Clone() interface.
>
> All of the previously abortable operations on the RGVAF (with the exception of
> ReadPixels()) can be made non-abortable, with no functional difference, due to
> the way the users of RGVAF function. These three users are
> WebMediaPlayerImpl/GpuVideoDecoder, RTCVideoDecoder, and RTCVideoEncoder, and
> they can be made non-abortable because:
>
> WebMediaPlayerImpl/GpuVideoDecoder:
> * Abort() is called from WebMediaPlayerImpl::Destroy(). It has no effect, as:
> * All the RGVAF entry points are called from the the RGVAF message loop
> from GpuVideoDecoder (except for ReadPixels()), so the Abort() has no
> effect on them.
>
> RTCVideoDecoder:
> * Abort() is called from RTCVideoDecoder::WillDestroyCurrentMessageLoop() for
> the RGVAF message loop. It has no effect, as:
> * Amost all the RGVAF entry points are called from the RGVAF message loop
> (except for ReadPixels()), so Abort() has no effect on them.
> * The other exception is CreateVideoDecodeAccelerator(), which is called from
> RTC's main thread. But as the Abort() is called from
> WillDestroyCurrentMessageLoop() for the RGVAF message loop itself, it is
> guaranteed to occur after any tasks posted to the RGVAF message loop by
> CreateVideoDecodeAccelerator() has completed, and so the Abort() has no
> effect.
>
> RTCVideoEncoder:
> * Abort() is called from RTCVideoDecoder::Release(). It has no effect, as:
> * All the RGVAF entry points are called from the RGVAF message loop.
>
> The only functional difference remaining is that making ReadPixels()
> non-abortable. This is preferable, as as long as a completed video accelerator
> texture is available, it should be readable. We also specify that all calls to
> ReadPixels must be made on the RGVAF message loop, like all other entry points,
> and leave it up to the users of ReadPixels() to handle thread trampolining if
> necessary.
>
> BUG=306333
> TEST=local build, run on CrOS snow; build, run unittests on desktop Linux
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247480
TBR=fischman@chromium.org,wuchengli@chromium.org,jamesr@chromium.org,jam@chromium.org,hshi@chromium.org,sheu@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=306333
Review URL: https://codereview.chromium.org/
145103004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247655 0039d316-1c4b-4281-b951-d872f2087c98