Suspects:

https://chromium-review.googlesource.com/c/chromium/src/+/1255152
https://chromium-review.googlesource.com/c/chromium/src/+/1257832

Sadrul, Hugo, can you PTAL?

My change is completely unrelated. I'd suspect Sadrul's change...

This is failing pretty consistently on Builders Linux Tests and linux-xenial-rel.

Example failure:
Traceback (most recent call last):
      File "/b/s/w/ir/third_party/catapult/telemetry/telemetry/testing/browser_test_case.py", line 39, in WrappedMethod
        method(self)
      File "/b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/scroll_unittest.py", line 115, in testScrollDistanceSlowWheel
        1000, 300, page_action.GESTURE_SOURCE_MOUSE, 100)
      File "/b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/actions/scroll_unittest.py", line 79, in _RunScrollDistanceTest
        self.assertAlmostEqual(distance, actual, delta=maxError + urlBarError)
    AssertionError: 1000 != 739 within 250 delta

I would also suspect the high-frequency synthetic gesture dispatch CL as the culprit.

Yep, I believe it's mine. I think the test is flaky ... the expectation seems suspect. I will bump up the error in the test.

What does "bump up the error" mean? Any objections to just reverting https://chromium-review.googlesource.com/c/chromium/src/+/1255152 (that was deemed the cause of these errors, right?) until you figure out what the problem is?

 Issue 892235  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ae26a2e41edaa334d60048b48c496062a4bb99c1

commit ae26a2e41edaa334d60048b48c496062a4bb99c1
Author: Marijn Kruisselbrink <mek@chromium.org>
Date: Thu Oct 04 17:55:42 2018

Revert "synthetic gesture: Allow high-frequency dispatch."

This reverts commit 581a728b2665c85e466408c2d53371abcb7f763e.

Reason for revert: Causing significant test flakiness in telemetry.internal.actions.scroll_unittest.ScrollActionTest.testScrollDistanceSlowWheel.

Original change's description:
> synthetic gesture: Allow high-frequency dispatch.
> 
> For synthesized scroll/drag/pinch gestures, dispatch the events
> at a high frequency (120Hz) so that there's at least one event in
> each frame. Dispatching events at a lower frequency (60Hz) means
> the timer can go out of sync with begin-frame, and so there can
> be frames where there was to event dispatch. Our telemetry code
> reports this as jank, which is incorrect. Dispatching at a higher
> frequency for the scroll/drag/pinch gestures resolves this issue.
> 
> BUG= 783034 
> 
> Change-Id: I1102f76ed743231cbb10fdb872e8c66f895fa223
> Reviewed-on: https://chromium-review.googlesource.com/c/1255152
> Reviewed-by: Victor Miura <vmiura@chromium.org>
> Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
> Reviewed-by: Lan Wei <lanwei@chromium.org>
> Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#596507}

TBR=sadrul@chromium.org,vmiura@chromium.org,lanwei@chromium.org,nzolghadr@chromium.org

Change-Id: I1e4d64dfc3b98a547c38f8f82a2dcd45141fd66b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  783034 ,  892036 
Reviewed-on: https://chromium-review.googlesource.com/c/1261972
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596748}
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_gesture.cc
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_gesture.h
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_gesture_controller.cc
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_gesture_controller.h
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_pointer_action.cc
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_pointer_action.h
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_tap_gesture.cc
[modify] https://crrev.com/ae26a2e41edaa334d60048b48c496062a4bb99c1/content/browser/renderer_host/input/synthetic_tap_gesture.h

Revering the CL

Oh, thank you mek@ for taking care of the revert.

The following revision refers to this bug:
  https://chromium.googlesource.com/catapult/+/de52d9ad295ecc6401de6d7cc3b468a0e8292308

commit de52d9ad295ecc6401de6d7cc3b468a0e8292308
Author: Sadrul Habib Chowdhury <sadrul@chromium.org>
Date: Fri Oct 05 13:16:25 2018

scroll: Allow for more errors.

Changing the frequency of scroll-event dispatch mean there are more
events being generated, and thus being queued/coalesced. So it is
possible for the scroll to not have reached the goal by the time the
test terminates. So allow for a little more distance from the target
for the slow-wheel unit-test.

BUG= chromium:892036 

Change-Id: Ifc7a6f79c51a15800fcd702d076237a4ef764049
Reviewed-on: https://chromium-review.googlesource.com/c/1264175
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>

[modify] https://crrev.com/de52d9ad295ecc6401de6d7cc3b468a0e8292308/telemetry/telemetry/internal/actions/scroll_unittest.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a4ac489299429d98c31e8b63ec13d9a248c5866b

commit a4ac489299429d98c31e8b63ec13d9a248c5866b
Author: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Date: Fri Oct 05 14:19:13 2018

Roll src/third_party/catapult 56216d7832a4..de52d9ad295e (1 commits)

https://chromium.googlesource.com/catapult.git/+log/56216d7832a4..de52d9ad295e


git log 56216d7832a4..de52d9ad295e --date=short --no-merges --format='%ad %ae %s'
2018-10-05 sadrul@chromium.org scroll: Allow for more errors.


Created with:
  gclient setdep -r src/third_party/catapult@de52d9ad295e

The AutoRoll server is located here: https://autoroll.skia.org/r/catapult-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

CQ_INCLUDE_TRYBOTS=luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel

BUG= chromium:892036 
TBR=sullivan@chromium.org

Change-Id: Ic8478361b73397bcad961ca65dc35681cf52910f
Reviewed-on: https://chromium-review.googlesource.com/c/1264625
Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#597104}
[modify] https://crrev.com/a4ac489299429d98c31e8b63ec13d9a248c5866b/DEPS