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

Review URL: https://codereview.chromium.org/143003012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246298 0039d316-1c4b-4281-b951-d872f2087c98
Disable compositing entries in about:flags for mac

Threaded compositing is now on by default on all macs. Disabling force
compositing mode and/or threaded compositing is no longer supported and
hence the option is now removed from about:flags.

BUG=336623

Review URL: https://codereview.chromium.org/143883009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246299 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246298
[MIPS] Set make_global_settings correctly for MIPS-Linux

Fix build regression for MIPS Linux that came with r245563.

BUG= build regression for MIPS Linux
TEST= build Chromium for MIPS Linux

Review URL: https://codereview.chromium.org/143963006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246300 0039d316-1c4b-4281-b951-d872f2087c98
Rebaseline and re-enable a11y tree tests for <dialog>.

They were disabled in r245116 to wait for Blink r165211
"Make ancestors of modal <dialog> inert" which has since
been rolled in.

BUG=329407
TBR=dominicc

Review URL: https://codereview.chromium.org/143973008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246301 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246301