All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=872150

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=6981973b8120414d3bb3781876be4621d1c247ea15a36910c29c71681a4a8482


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

Android Nexus5X WebView Perf

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/16cf6da4640000

📍 Found significant differences after each of 3 commits.
https://pinpoint-dot-chromeperf.appspot.com/job/16cf6da4640000

[auto] Update FlagExpectations for LayoutNG by kojii@chromium.org
https://chromium.googlesource.com/chromium/src/+/bf2febf8e4aa77332f2d5d97e8d319550ff7a104
2175 → 2135 (-40.34)

Roll clang 337439:338452. by rnk@google.com
https://chromium.googlesource.com/chromium/src/+/cc14e55b5cd9359e09aa9b8aa8795b100031abfb
2105 → 1692 (-413.8)

[ios] Fix stale snapshotting and snapshots flickering blank by edchin@chromium.org
https://chromium.googlesource.com/chromium/src/+/081eb1d1bad7865b3774941414ffa2a14eef7586
1692 → 1752 (+60.17)

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

My CL below lives entirely in iOS so I doubt it affected the performance of Android Nexus5X WebView. Passing this onto kojii@ 

[ios] Fix stale snapshotting and snapshots flickering blank by edchin@chromium.org
https://chromium.googlesource.com/chromium/src/+/081eb1d1bad7865b3774941414ffa2a14eef7586
1692 → 1752 (+60.17)

My CL updates flag-specific TestExpectation only, no code changes.

rnk@?

This looks like a performance regression in a compiler update from August. We don't have the bandwidth to investigate every such change.