All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=751989

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=80dd870ec07613e2416a13cd2e926b0e3b1d1f051c47202ab7a9aa733df36f5b


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

android-nexus5
android-webview-nexus6
chromium-rel-mac11
chromium-rel-mac11-air
linux-release

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/8972297567087093008

This is a suspiciously large improvement, I guess something broke.

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

Hi shend@chromium.org, the bisect results pointed to your CL, please take a look at the
results.


=== BISECT JOB RESULTS ===
Perf regression found with culprit

Suspected Commit
  Author : Darren Shen
  Commit : 744f09725b57a1d3e0640c300045946756d0774d
  Date   : Thu Jul 27 07:23:08 2017
  Subject: Reduce blink_perf.css cycle time.

Bisect Details
  Configuration: mac_air_perf_bisect
  Benchmark    : blink_perf.css
  Metric       : Document::updateStyle/Document::updateStyle
  Change       : 98.91% | 180.758114493 -> 1.9660984127

Revision             Result                    N
chromium@489868      180.758 +- 1.77096        6      good
chromium@489872      189.241 +- 3.51632        6      good
chromium@489874      183.066 +- 2.36577        6      good
chromium@489875      1.9859 +- 0.0436391       6      bad       <--
chromium@489876      1.94848 +- 0.0284641      6      bad
chromium@489883      1.96813 +- 0.068501       6      bad
chromium@489897      1.9661 +- 0.0453172       6      bad

To Run This Test
  src/tools/perf/run_benchmark -v --browser=release --output-format=chartjson --upload-results --pageset-repeat=1 --also-run-disabled-tests blink_perf.css

More information on addressing performance regressions:
  http://g.co/ChromePerformanceRegressions

Debug information about this bisect:
  https://chromeperf.appspot.com/buildbucket_job_status/8972297567087093008


For feedback, file a bug with component Speed>Bisection

That patch fixes the cycle time regression introduced in  crbug.com/749012  by reducing the size of test cases. You can see that these were new test cases added recently but were found to be too resource intensive, so we scaled them down, hence the "improvement".