cc: CompositorTimingHistory throughput UMAs

This adds the following metrics:

1) BeginMainFrameIntervalCritical:
     Commit rate, aborted or not, with the critical flag set.
2) BeginMainFrameIntervalNotCritical:
     Commit rate, aborted or not, without the critical flag set.
2) CommitInterval:
     Draw rate of new active trees.
3) DrawInterval:
     Draw rate of the compositor.

Each metric is only reported when
that stage is in a continually active
state.

BUG=477012
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1460923002

Cr-Commit-Position: refs/heads/master@{#361743}
6 files changed