Revert of TaskGraphRunner Group support

Revert of TaskGraphRunner Group support (patchset #11 id:340001 of https://codereview.chromium.org/1489233003/ )

Reason for revert:
This might cause test failure on SynchronousTaskGraphRunner/SingleThreadTaskGraphRunnerTest/
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=SynchronousTaskGraphRunner%2FSingleThreadTaskGraphRunnerTest%2F0.Priority&testType=cc_unittests

Original issue's description:
> TaskGraphRunner Group support
>
> Adds a group to TaskGraphRunner, this can be used by an
> implementation along with priority in order to decide how to execute
> tasks.
>
> This is a prerequisite patch for thread affinity changes which are
> coming in a follow-up.
>
> This patch causes a moderate (~15%) regression in cc_perftests for TaskGraphRunner.
>
> The main regressions I'm seeing are:
>
> In ScheduleTasks, we're seeing an additional 3% time spent in operator[] for the two new maps vs ToT.
>
> We're also seeing an additional 5.5% of time spent in test code which builds the task graph.
>
> Other regressions are less clear, but probably have to do with the additional cost of ScheduleTasks in the function body itself (inlined looping).
>
> BUG=
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/05ca4bc9df381e6345f9cf7ee29cdfa075be30c4
> Cr-Commit-Position: refs/heads/master@{#365140}

TBR=reveman@chromium.org,sievers@chromium.org,ericrk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/816bb5c6abd09d3fc79d3e76152424092f0735d6
Cr-Commit-Position: refs/heads/master@{#365147}

[yoichio, 2015-12-15 04:26:44]

Created Revert of TaskGraphRunner Group support

[commit-bot: I haz the power, 2015-12-15 04:27:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1521423003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1521423003/1

[commit-bot: I haz the power, 2015-12-15 04:29:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-12-15 04:30:07]

Description was changed from

==========
Revert of TaskGraphRunner Group support (patchset #11 id:340001 of
https://codereview.chromium.org/1489233003/ )

Reason for revert:
This might cause test failure on
SynchronousTaskGraphRunner/SingleThreadTaskGraphRunnerTest/
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=Syn...

Original issue's description:
> TaskGraphRunner Group support
> 
> Adds a group to TaskGraphRunner, this can be used by an
> implementation along with priority in order to decide how to execute
> tasks.
> 
> This is a prerequisite patch for thread affinity changes which are
> coming in a follow-up.
> 
> This patch causes a moderate (~15%) regression in cc_perftests for
TaskGraphRunner.
> 
> The main regressions I'm seeing are:
> 
> In ScheduleTasks, we're seeing an additional 3% time spent in operator[] for
the two new maps vs ToT.
> 
> We're also seeing an additional 5.5% of time spent in test code which builds
the task graph.
> 
> Other regressions are less clear, but probably have to do with the additional
cost of ScheduleTasks in the function body itself (inlined looping).
> 
> BUG=
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
> 
> Committed: https://crrev.com/05ca4bc9df381e6345f9cf7ee29cdfa075be30c4
> Cr-Commit-Position: refs/heads/master@{#365140}

TBR=reveman@chromium.org,sievers@chromium.org,ericrk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
==========

to

==========
Revert of TaskGraphRunner Group support (patchset #11 id:340001 of
https://codereview.chromium.org/1489233003/ )

Reason for revert:
This might cause test failure on
SynchronousTaskGraphRunner/SingleThreadTaskGraphRunnerTest/
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=Syn...

Original issue's description:
> TaskGraphRunner Group support
>
> Adds a group to TaskGraphRunner, this can be used by an
> implementation along with priority in order to decide how to execute
> tasks.
>
> This is a prerequisite patch for thread affinity changes which are
> coming in a follow-up.
>
> This patch causes a moderate (~15%) regression in cc_perftests for
TaskGraphRunner.
>
> The main regressions I'm seeing are:
>
> In ScheduleTasks, we're seeing an additional 3% time spent in operator[] for
the two new maps vs ToT.
>
> We're also seeing an additional 5.5% of time spent in test code which builds
the task graph.
>
> Other regressions are less clear, but probably have to do with the additional
cost of ScheduleTasks in the function body itself (inlined looping).
>
> BUG=
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/05ca4bc9df381e6345f9cf7ee29cdfa075be30c4
> Cr-Commit-Position: refs/heads/master@{#365140}

TBR=reveman@chromium.org,sievers@chromium.org,ericrk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/816bb5c6abd09d3fc79d3e76152424092f0735d6
Cr-Commit-Position: refs/heads/master@{#365147}
==========

[commit-bot: I haz the power, 2015-12-15 04:30:07]

Patchset 1 (id:??) landed as
https://crrev.com/816bb5c6abd09d3fc79d3e76152424092f0735d6
Cr-Commit-Position: refs/heads/master@{#365147}