All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=911065

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=cc4c0bfd3089f32273108775c50d8e5d9612bae105d53a54f541eaee72ceb5f0


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

Win 7 Perf
mac-10_12_laptop_low_end-perf
mac-10_13_laptop_high_end-perf

v8.browsing_desktop - Benchmark documentation link:
  None

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/168e1dfc140000

😿 Pinpoint job stopped with an error.
https://pinpoint-dot-chromeperf.appspot.com/job/168e1dfc140000

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

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/12f2653c140000

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/115445d8140000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/115445d8140000

[v8] Add Mac to script streaming field trial by leszeks@chromium.org
https://chromium.googlesource.com/chromium/src/+/984c9422cefcd565e6ccef6a7316ba2488107e93
v8-gc-scavenger: 3.796 → 4.376 (+0.5796)

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

Benchmark documentation link:
  None

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/12f2653c140000

[v8] Add Mac to script streaming field trial by leszeks@chromium.org
https://chromium.googlesource.com/chromium/src/+/984c9422cefcd565e6ccef6a7316ba2488107e93
v8-gc-total: 226.4 → 363.3 (+136.9)

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

Benchmark documentation link:
  None

WAI consequence of increased parallelism.

Oh wait, this is GC time, not memory use. Un-WAI.

+petermarshall as memory sheriff, I feel like this is a consequence of increased "busyness" at startup.

Did the same thing happen when this was turned on on other platforms?

I haven't seen it on other platforms, no, but could be that other active flags changed in between.