The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/911bded93ce094463ca02121861c4c036b5743df

commit 911bded93ce094463ca02121861c4c036b5743df
Author: David Bokan <bokan@chromium.org>
Date: Tue Nov 27 23:23:32 2018

Add Feature and about:flag for root scroller

This will be used to allow a kill-switch for the feature post-launch as
well as help debugging.

Bug:  903263 
Change-Id: Icaf0b9ea4f28f9abddfa67f88fc6759aca812ec3
Reviewed-on: https://chromium-review.googlesource.com/c/1349476
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611404}
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/chrome/browser/about_flags.cc
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/chrome/browser/flag-metadata.json
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/content/child/runtime_features.cc
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/third_party/blink/common/features.cc
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/third_party/blink/public/common/features.h
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/third_party/blink/public/platform/web_runtime_features.h
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/third_party/blink/renderer/platform/exported/web_runtime_features.cc
[modify] https://crrev.com/911bded93ce094463ca02121861c4c036b5743df/tools/metrics/histograms/enums.xml