Revert 202363 "cc: Cancel and re-prioritize worker pool tasks."

Revert 202363 "cc: Cancel and re-prioritize worker pool tasks."

> cc: Cancel and re-prioritize worker pool tasks.
> 
> This adds a task graph interface to the worker pool and
> implements a simple queue instance of this interface for
> use by the tile manager.
> 
> The task graph interface can be used describe more
> complicated task dependencies in the future and
> provides the immediate benefit of seamlessly being
> able to cancel and re-prioritize tasks.
> 
> BUG=178974
> 
> Review URL: https://chromiumcodereview.appspot.com/14689004

TBR=reveman@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202736

[ramant (doing other things), 2013-05-29 01:28:09]

Committed patchset #1 manually as r202736.