The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/04ce77fc2727d5100b89719d7bd0256797b6dfa4

commit 04ce77fc2727d5100b89719d7bd0256797b6dfa4
Author: nzolghadr <nzolghadr@chromium.org>
Date: Fri Jun 02 15:37:44 2017

Add TimeToScrollUpdateSwapBegin2 to UKM

Report TimeToScrollUpdateSwapBegin2 via UKM
and also add the testing mechanisms in
render_widget_host_latency_tracker_unittest

BUG= 723677 , 728707

Review-Url: https://codereview.chromium.org/2888153002
Cr-Commit-Position: refs/heads/master@{#476670}

[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/chrome/browser/chrome_content_browser_client.cc
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/chrome/browser/chrome_content_browser_client.h
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/components/ukm/public/ukm_recorder.h
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/content/browser/renderer_host/input/render_widget_host_latency_tracker.h
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/content/browser/renderer_host/input/render_widget_host_latency_tracker_unittest.cc
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/content/public/browser/content_browser_client.cc
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/content/public/browser/content_browser_client.h
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/tools/metrics/ukm/ukm.xml
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/ui/latency/latency_tracker.cc
[modify] https://crrev.com/04ce77fc2727d5100b89719d7bd0256797b6dfa4/ui/latency/latency_tracker.h