Revert of Reland: Implement and test task runners in RasterWorkerPool. (patchset...

Revert of Reland: Implement and test task runners in RasterWorkerPool. (patchset #9 id:160001 of https://codereview.chromium.org/1254003003/ )

Reason for revert:
Typo in thread names. It breaks telemetry tests data.

Original issue's description:
> Reland: Implement and test task runners in RasterWorkerPool.
>
> This CL moves RasterWorkerPool outside render_thread_impl.h and
> in its own file, implements TaskRunner and SequencedTaskRunner
> on top of it and properly tests the two implementations.
>
> BUG=
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/6526c209494a5176f82b5f400fd1e66a426c840f
> Cr-Commit-Position: refs/heads/master@{#341827}

TBR=dalecurtis@chromium.org,piman@chromium.org,reveman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1273593002

Cr-Commit-Position: refs/heads/master@{#341842}