Sahel, could you take a look on this?
A test track-scroll.html which you introduced seems to fail on Mac.
https://chromium.googlesource.com/chromium/src/+/abe21f39a3cc131204de7fea6fc000baf53bcb27

It's lighting up Mac on the flakiness dashboard
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=fast%2Fscroll-behavior%2Fsmooth-scroll%2Ftrack-scroll.html&testType=webkit_layout_tests

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/36261ec5ea1bc5461dad64d119d3edebfac0871e

commit 36261ec5ea1bc5461dad64d119d3edebfac0871e
Author: David Grogan <dgrogan@chromium.org>
Date: Thu Jun 21 21:21:48 2018

Sheriff: Disable smooth-scroll/track-scroll.html on mac

TBR=anthonyvd@chromium.org

Bug: 854910
Change-Id: Ibc6fd782f7995a784f043f5d24c488d6c1aa38f5
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1110885
Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: David Grogan <dgrogan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569378}
[modify] https://crrev.com/36261ec5ea1bc5461dad64d119d3edebfac0871e/third_party/WebKit/LayoutTests/TestExpectations

What about external/wpt/orientation-sensor/AbsoluteOrientationSensor-iframe-access.https.html?
Flaked for me in https://ci.chromium.org/p/chromium/builders/luci.chromium.try/mac_chromium_rel_ng/78128

I'm disabling that now