All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=855473

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=90e945f43c0afd483afc4c2b672e1337e098605b1a152ed64018462825f89b3c


Bot(s) for this bug's original alert(s):

android-nexus5
android-one

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/12cd2fbb240000

📍 Found significant differences after each of 2 commits.
https://pinpoint-dot-chromeperf.appspot.com/job/12cd2fbb240000

Surface synchronization: Plumb more things through RenderFrameMetadata by fsamuel@chromium.org
https://chromium.googlesource.com/chromium/src/+/4576fad344baac5eb8821459489a9c0f792576e9
1.34 → 1.413 (+0.07266)

Surface synchronization: Plumb has_transparent_background by fsamuel@chromium.org
https://chromium.googlesource.com/chromium/src/+/d2a810ba3b6d344962623aeccc4917d80ddf6750
1.418 → 1.435 (+0.01742)

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

 Issue 855510  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0f108c08b8916d7915aaecca25c365d24f6438aa

commit 0f108c08b8916d7915aaecca25c365d24f6438aa
Author: Fady Samuel <fsamuel@chromium.org>
Date: Mon Jun 25 20:19:50 2018

Surface Synchronization: Don't ship RenderFrameMetadata on change in scroll

We don't need to ship updated RenderFrameMetadata on change in root scroll
offset. Shipping RenderFrameMetadata is expensive and so we should minimize
shipping them to the browser process as it also involves synchronization
with Viz.

We initially decided to plumb this value via RenderFrameMetadata in order
to properly support the overscroll glow on Android but this turned out to
be too expensive and so we are now investigating ways to compute the
overscroll glow at least partially in the renderer.

Bug:  672962 ,  855473 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I139f773eaf673785fec04c9f989abb36e0941ad9
Reviewed-on: https://chromium-review.googlesource.com/1113799
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570153}
[modify] https://crrev.com/0f108c08b8916d7915aaecca25c365d24f6438aa/cc/trees/render_frame_metadata.cc

It looks like the CL I landed in #5 has brought the performance much closer to where it was previously. I'm going to go ahead and mark this as fixed.