All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=898877

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=d2f867d7ce524641da48723a34f73699fdc3d26425d54efbbbeae3b0275ab8ca


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

Android Nexus5X WebView Perf
android-nexus5x-perf

rendering.mobile - Benchmark documentation link:
  https://bit.ly/rendering-benchmarks

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/16adb726e40000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/16adb726e40000

Use a special display item client for scrolling background by wangxianzhu@chromium.org
https://chromium.googlesource.com/chromium/src/+/0ceb353a7cea46198a109af7737f6a6c1b4fee73
thread_raster_cpu_time_per_frame: 0.1396 → 0.2802 (+0.1406)

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

Benchmark documentation link:
  https://bit.ly/rendering-benchmarks

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/13179e16e40000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/13179e16e40000

Revert "viz: Throttle begin-frames when gpu is busy." by sadrul@chromium.org
https://chromium.googlesource.com/chromium/src/+/3629d825012de4e1ce8cad1a2be9b654c7b01b6a
tasks_per_frame_total_all: 61.26 → 127.8 (+66.56)

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

Benchmark documentation link:
  https://bit.ly/rendering-benchmarks

Some alerts in https://chromeperf.appspot.com/group_report?bug_id=898877 are not caused by my CL, but the revert in #c5. I'm marking these alerts "ignored".

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2779a9b0df225a3e2ca284ab1d076f4dcd090c31

commit 2779a9b0df225a3e2ca284ab1d076f4dcd090c31
Author: Xianzhu Wang <wangxianzhu@chromium.org>
Date: Fri Oct 26 22:38:48 2018

[PE] Fix raster cpu regression of crrev.com/c/1297131

The regression was caused by 1px bigger visual rect of the
scrolling background.

Now snap PaintLayerScrollableArea::ScrollingBackgroundDisplayItemClient::VisualRect()
to whole pixels. This matches the original original visual rect
of scrolling background before crrev.com/c/1297131.

Bug:  898877 

Change-Id: I7b8df7850a5a7fb680ea903064247d72fa9d9278
Reviewed-on: https://chromium-review.googlesource.com/c/1300593
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603228}
[modify] https://crrev.com/2779a9b0df225a3e2ca284ab1d076f4dcd090c31/third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc