All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=911587

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=09606a07d59b97ae9ea37c80849b4e15cb8c2f7c199e5ead05397847136c1f4e


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

Win 7 Perf

blink_perf.shadow_dom - Benchmark documentation link:
  https://bit.ly/blink-perf-benchmarks

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/127c9b2c140000

😿 Pinpoint job stopped with an error.
https://pinpoint-dot-chromeperf.appspot.com/job/127c9b2c140000

All of the runs failed. The most common error (19/20 runs) was:
SwarmingTestError: The test failed. No Python exception was found in the log.

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/12fd5925940000

Requesting another pinpoint run.

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/12fd5925940000

Guard fast flat tree traversal (fftt) by runtime flag by hayato@chromium.org
https://chromium.googlesource.com/chromium/src/+/d9cba271a2ad1761f12731887bb4427fa7719da2
v1-mutate-shallow-tree-then-slot-flatten: 19.96 → 23.19 (+3.226)

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

Benchmark documentation link:
  https://bit.ly/blink-perf-benchmarks

It looks an *expected* regression. I should have clarified that in the CL.