GitLab

Add StartDataCollection/StopDataCollection to start/stop gathering
the data reported by ui::ThroughputTracker. The API will be used
by tast tests via AutotestPrivateAPI to calculate animation frame
rate sub score.

Bug: 1098555
Change-Id: I1e871fd6575f54101bbe701d42960d5259b749e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2305013
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792749}