Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner directly. (https://codereview.chromium.org/141163019/)

Reason for revert:
Bad file mode for task_graph_runner.h:

/b/build/slave/Linux_ChromiumOS/build/src/cc/resources/task_graph_runner.h: Must not have executable bit set


http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Full/builds/31393/steps/check_perms/logs/stdio

Original issue's description:
> cc: Remove WorkerPool class and instead use TaskGraphRunner directly.
> 
> Removes the unnecessary WorkerPool layer. This makes the job
> of the TaskGraphRunner more clear and will allow us to remove
> some complexity and unnecessary heap allocations from the
> RasterWorkerPool code in follow up patches.
> 
> Also moves the kNumRasterTasks switch to content/.
> 
> Refactor only, no changes in behavior.
> 
> BUG=331844
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=246284

TBR=vmpstr@chromium.org,alokp@chromium.org,sohan.jyoti@samsung.com,jamesr@chromium.org,piman@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=331844
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=246298

[Mattias Nissler (ping if slow), 2014-01-22 11:40:00]

Created Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner
directly.

[commit-bot: I haz the power, 2014-01-22 11:40:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mnissler@chromium.org/143003012/1

[commit-bot: I haz the power, 2014-01-22 11:41:01]

Change committed as 246298