Revert of cc: Cleanup internal::WorkerPoolTaskClient interface. (https://codereview.chromium.org/170783007/)

Reason for revert:
Speculative revert. Suspecting that this CL may be causing a DCHECK to fire on Android in PixelBufferRasterWorkerPool::ScheduleMoreTasks(

http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/18755/steps/slave_steps/logs/stdio

Original issue's description:
> cc: Cleanup internal::WorkerPoolTaskClient interface.
> 
> ::CompleteOnOriginThread is now called when RasterWorkerPool has
> completed all necessary initialization of resource, including
> texture uploads. This improves the WorkerPoolTask/Client interface
> significantly and will allow better resource recycling once
> ::RunReplyOnOriginThread is removed.
> 
> BUG=269841
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=252790

TBR=vmpstr@chromium.org,alokp@chromium.org,sergeyberezin@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=269841

Review URL: https://codereview.chromium.org/176403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252807 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252807