All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=795001

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=59e2116c9d7b931a0184c8fb7ddde36c1b7eee58b11628cc65a5245cc19b2c02


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

android-nexus5
android-nexus5X
android-nexus6

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/8960213369018130784

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

Hi sunxd@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 : sunxd
  Commit : 269a3a39c49562eac9e10b8fd3623fc93d3a874a
  Date   : Tue Dec 12 04:03:11 2017
  Subject: Enable composited border radius scrolling

Bisect Details
  Configuration: android_nexus5X_perf_bisect
  Benchmark    : system_health.common_mobile
  Metric       : cpu_time_percentage_avg/browse_media/browse_media_youtube
  Change       : 5.89% | 0.377695382953 -> 0.399954239516

Revision             Result                      N
chromium@523303      0.377695 +- 0.00641447      6      good
chromium@523318      0.376665 +- 0.00356641      6      good
chromium@523320      0.36949 +- 0.0070116        6      good
chromium@523321      0.37575 +- 0.00467427       6      good
chromium@523322      0.394161 +- 0.00892803      6      bad       <--
chromium@523325      0.398557 +- 0.00760858      6      bad
chromium@523332      0.3988 +- 0.00268825        6      bad
chromium@523360      0.399954 +- 0.00473479      6      bad

To Run This Test
  src/tools/perf/run_benchmark -v --browser=android-chromium --output-format=chartjson --upload-results --pageset-repeat=1 --also-run-disabled-tests --story-filter=browse.media.youtube system_health.common_mobile

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

Debug information about this bisect:
  https://chromeperf.appspot.com/buildbucket_job_status/8960213369018130784


For feedback, file a bug with component Speed>Bisection

Issue 794997 has been merged into this issue.

I think the regression is expected since we now composite more layers: we used to force border-radius elements scroll on main, but the patch make them use the fast impl scrolling path, and the cost is to composite these border-radius elements.

Thanks for the explanation, sunxd! I'm WontFix-ing since this is a small regression and the tradeoff is explained, but feel free to reopen if you want to work on speeding this path up.