Tests in question are

fast/events/middleClickAutoscroll-nested-divs.html
fast/events/middleClickAutoscroll-latching.html
fast/events/middleClickAutoscroll-nested-divs-forbidden.html

The first 2 are already disabled, the last is not yet, I am disabling it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ecb1b145d74b627061f77a535f4df56536fda486

commit ecb1b145d74b627061f77a535f4df56536fda486
Author: vitaliii <vitaliii@chromium.org>
Date: Thu Aug 09 09:02:39 2018

Disable flaky f/e/middleClickAutoscroll-nested-divs-forbidden.html (Mac)

TBR=sahel@chromium.org
NOTRY=true

Bug:  872635 , 872632 
Change-Id: I59bb656ad0047c7391d96a6b59e1358af91a7b17
Reviewed-on: https://chromium-review.googlesource.com/1169002
Reviewed-by: vitaliii <vitaliii@chromium.org>
Commit-Queue: vitaliii <vitaliii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581832}
[modify] https://crrev.com/ecb1b145d74b627061f77a535f4df56536fda486/third_party/WebKit/LayoutTests/TestExpectations

Please have a look!

 Issue 872328  has been merged into this issue.

The tests are consistently failing on Mac since middleclickautoscroll fling on Mac has recently switched to use ui::Compositor for fling progress and OnAnimationStep is not called while running webkit_layout_tests:

https://chromium-review.googlesource.com/1149612 is the root cause of the test failures, and re-commenting the code in fling_scheduler_mac.mm (to fall back in none-viz path) fixes the issue.

Note that the bug only happens while running layout tests, manual autoscrolls and browsertests are working properly.

Cced ccameron@ and jonross@ for more investigation.

If I'm reading the Flakiness Dashboard (https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=virtual%2Fuser-activation-v2%2Ffast%2Fevents%2FmiddleClickAutoscroll-latching.html) correctly this test is also flaky on Mac 10.10 as well as Linux and Win7 dbg.

I'm going to check those other OS's. sahel@ please correct me if I'm misreading the dashboard. Also, we may want to consider merging  issue 873435  and issue 827209 into this bug.

There are two issues here:
1-middleClickAutoscroll-latching.html is flaky on debug builds and it is not mac only.
2-middleClickAutoscroll- tests started to consistently fail/timeout on mac after landing https://chromium-review.googlesource.com/1149612
The owner is ooo and I am talking to ccameron@ to see what the state of the Viz on Mac is and if it is ok to revert this cl.

Viz on Mac is ready for Finch trials. However the patch referenced in #7 is required to support fling scrolling for Viz on Mac.

Considering the webkit_layout_tests are failing after this change due to not calling OnAnimationStep, and other tests covering the feature are fine. This makes me think that the webkit_layout_tests are now just incorrect and need updating.

Can we have them marked as expecting failure until they can be reworked?

>Considering the webkit_layout_tests are failing after this change due to not calling OnAnimationStep, and other tests covering the feature are fine. This makes me think that the webkit_layout_tests are now just incorrect and need updating.

The tests are fine on all other platforms and OnAnimationStep on none-mac platforms gets called properly. The issue being mac only makes the tests unlikely to be incorrect. I rewrote one of the tests to use gpu-benchmarking, the same issue exists with the new test as well.