All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=591743

Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?keys=agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgIDA34eZrgkM


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

android-nexus6

=== Auto-CCing suspected CL author wangxianzhu@chromium.org ===

Hi wangxianzhu@chromium.org, the bisect results pointed to your CL below as possibly
causing a regression. Please have a look at this info and see whether
your CL be related.


===== BISECT JOB RESULTS =====
Status: completed


===== SUSPECTED CL(s) =====
Subject : Partly revert of Conditionally create PaintLayer's scrollable area object (patchset #8 id:140001 of https://codereview.chromium.org/1643663002/ )
Author  : wangxianzhu
Commit description:
  
Reason for revert:
Caused bug 591045. CompositedLayerMapping and ScrollingCoordinator don't expect
scrollableArea of a layer to disappear.

Revert functional changes, but keep refactories.

BUG=591045

Original issue's description:
> Conditionally create PaintLayer's scrollable area object
>
> BUG= 467721 
>
> Committed: https://crrev.com/e3e7bae15616191d743019b9a5b77ac201aec20e
> Cr-Commit-Position: refs/heads/master@{#378247}

TBR=chrishtr@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 467721 

Review URL: https://codereview.chromium.org/1755243002

Cr-Commit-Position: refs/heads/master@{#378845}
Commit  : b772a3d31c12361e22a8d6950cbef821ac3dc7d5
Date    : Wed Mar 02 21:54:56 2016


===== TESTED REVISIONS =====
Revision                Mean Value  Std. Dev.   Num Values  Good?
chromium@378821         0.154682    0.002421    5           good
chromium@378834         0.147877    0.002918    5           good
chromium@378840         0.146135    0.002371    5           good
chromium@378843         0.147947    0.004596    5           good
chromium@378844         0.149213    0.004877    5           good
chromium@378845         0.114922    0.001567    5           bad
chromium@378846         0.115378    0.002439    5           bad
chromium@378870         0.113054    0.001114    5           bad

Bisect job ran on: android_nexus6_perf_bisect
Bug ID: 591743

Test Command: src/tools/perf/run_benchmark -v --browser=android-chromium --output-format=chartjson --also-run-disabled-tests blink_perf.events
Test Metric: hit-test-lots-of-layers/hit-test-lots-of-layers
Relative Change: 26.91%
Score: 99.9

Buildbot stdio: http://build.chromium.org/p/tryserver.chromium.perf/builders/android_nexus6_perf_bisect/builds/2000
Job details: https://chromeperf.appspot.com/buildbucket_job_status/9019186964412652656


| O O | Visit http://www.chromium.org/developers/speed-infra/perf-bug-faq
|  X  | for more information addressing perf regression bugs. For feedback,
| / \ | file a bug with label Cr-Tests-AutoBisect.  Thank you!

The performance just returned to the original level before the original CL partly reverted by e3e7bae15616191d743019b9a5b77ac201aec20e.

Glad to know that conditionally creating scrollable area for layers can really improve performance. Will still try it without breaking things.