All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=659535

Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?keys=agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgICgvZznuQoM


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

chromium-rel-win8-dual

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/8997749479431331840

=== Auto-CCing suspected CL author rune@opera.com ===

Hi rune@opera.com, 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 : Move TreeBoundaryCrossingScopes to StyleEngine.
Author  : rune
Commit description:
  
This is split out of the work for async stylesheet updates [1], but is
also part of the work on componentized style resolving in general.

The moved resetAuthorStyle method on StyleEngine may soon be gone
altogether as it does so in [1].

The plan is that TreeBoundaryCrossingScopes will also be completely
gone when we remove support for Shadow DOM v0. For Shadow DOM v1 we can
look up the scoped resolvers for the affecting scopes directly like we
already do in StyleResolver::matchScopedRules for the pure v1 case.

The documentation of the special casing of VTT and custom pseudo
elements is updated to not suggest that these rules are handled as part
of boundary crossing scopes as the current solution is better once v0
shadows go away.

[1] https://codereview.chromium.org/1913833002

R=meade@chromium.org
BUG= 567021 ,401359

Review-Url: https://codereview.chromium.org/2443933002
Cr-Commit-Position: refs/heads/master@{#427284}
Commit  : c65b3eb1cc989a7a13813e4ef68042ae2e030c22
Date    : Tue Oct 25 06:10:45 2016


===== TESTED REVISIONS =====
Revision         Mean     Std Dev    N  Good?
chromium@427281  180.323  0.743012   5  good
chromium@427283  180.213  0.809839   5  good
chromium@427284  28.4255  0.0628648  5  bad    <--
chromium@427287  28.1923  0.195739   5  bad
chromium@427293  28.461   0.0828702  5  bad

Bisect job ran on: win_8_perf_bisect
Bug ID: 659535

Test Command: src/tools/perf/run_benchmark -v --browser=release --output-format=chartjson --upload-results --pageset-repeat=1 --also-run-disabled-tests blink_perf.dom
Test Metric: select-single-remove/select-single-remove
Relative Change: 84.22%
Score: 99.9

Buildbot stdio: http://build.chromium.org/p/tryserver.chromium.perf/builders/win_8_perf_bisect/builds/2262
Job details: https://chromeperf.appspot.com/buildbucket_job_status/8997749479431331840


Not what you expected? We'll investigate and get back to you!
  https://chromeperf.appspot.com/bad_bisect?try_job_id=5887593911156736

| 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 component Tests>AutoBisect.  Thank you!

https://codereview.chromium.org/2452733004/

Fix: https://codereview.chromium.org/2452733004/

The graph will not recover fully with that fix because of  issue 659647 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/72f115c8f71b04929130f9a71ff9f217cb8cbc4f

commit 72f115c8f71b04929130f9a71ff9f217cb8cbc4f
Author: rune <rune@opera.com>
Date: Thu Oct 27 05:55:07 2016

Removed unnecessary rule feature reset when no ScopedStyleResolver.

Resetting rule features when a shadow tree did not contain any
stylesheets, and hence didn't have a ScopedStyleResolver, caused a
performance regression in the select-single-remove performance test.

UA shadow trees typically don't have any stylesheets.

This is a regression from [1].

[1] https://codereview.chromium.org/2443933002

R=meade@chromium.org
BUG= 659535 
TEST=PerformanceTests/DOM/select-single-remove.html

Review-Url: https://codereview.chromium.org/2452733004
Cr-Commit-Position: refs/heads/master@{#427949}

[modify] https://crrev.com/72f115c8f71b04929130f9a71ff9f217cb8cbc4f/third_party/WebKit/Source/core/dom/StyleEngine.cpp

Marking as fixed, although the graphs won't recover until  issue 659647  is fixed.

Issue 659586 has been merged into this issue.