[Blink-Scheduler] Distinguish between normal and foreground-only renderers for monitoring load.

[Blink-Scheduler] Distinguish between normal and foreground-only renderers for monitoring load.

This CL introduces the concept of a foreground-only renderer to the Blink
RendererScheduler. This allows the RendererScheduler to distinguish between
normal and foreground-only renderers (like extension renderers) while collecting
main thread load metrics.

Since this changes the semantics of the
RendererScheduler.ForegroundRendererMainThreadLoad histogram (it no longer
includes foreground-only renderers), it is replaced with
RendererScheduler.ForegroundRendererMainThreadLoad2. Also,
RendererScheduler.ForegroundOnlyRendererMainThreadLoad hisogram is introduced to
collect main thread load metrics for foreground-only renderers.

[karandeepb, 2017-05-03 22:15:31]

The CQ bit was checked by karandeepb@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-05-03 22:16:12]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[karandeepb, 2017-05-03 22:49:52]

Description was changed from

==========
[Blink-Scheduler] Distinguish between normal and foreground-only renderers for
monitoring load.
==========

to

==========
[Blink-Scheduler] Distinguish between normal and foreground-only renderers for
monitoring load.

This CL introduces the concept of a foreground-only renderer to the Blink
RendererScheduler. This allows the RendererScheduler to distinguish between
normal and foreground-only renderers (like extension renderers) while collecting
main thread load metrics.

Since this changes the semantics of the
RendererScheduler.ForegroundRendererMainThreadLoad histogram (it no longer
includes foreground-only renderers), it is replaced with
RendererScheduler.ForegroundRendererMainThreadLoad2. Also,
RendererScheduler.ForegroundOnlyRendererMainThreadLoad hisogram is introduced to
collect main thread load metrics for foreground-only renderers.
==========

[commit-bot: I haz the power, 2017-05-03 23:25:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-03 23:25:35]

Dry run: Try jobs failed on following builders:
  win_chromium_x64_rel_ng on master.tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[karandeepb, 2017-05-17 04:27:45]

The CQ bit was checked by karandeepb@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-05-17 04:29:02]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-17 05:52:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-17 05:52:36]

Dry run: Try jobs failed on following builders:
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)