The tests are:

virtual/outofblink-cors-ns/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-simple.html
virtual/outofblink-cors-ns/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-synconworker.html
virtual/outofblink-cors/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-aborted.html
virtual/threaded/fast/scrolling/overflow-scrollability.html

I'm not sure if this is the result of switching to 10.13 or not, but I suspect it is.

Suppressing failures for now while investigating (pls don't revert the change).

It looks like these tests are all really slow (but not marked as such) and were almost timing out before. Marking them as Slow should be sufficient.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5daa8048adfc79c170d639eeda8dc96eeab16fb7

commit 5daa8048adfc79c170d639eeda8dc96eeab16fb7
Author: Dirk Pranke <dpranke@chromium.org>
Date: Tue Jul 31 23:38:45 2018

Mark a few webkit_layout_tests as Slow.

The recent switch from running the webkit_layout_tests on 10.12 by default
to 10.13 has revealed a few tests that were almost timing out before and
are now timing out on 10.13 due to the slightly slower configurations.

This CL marks the four tests as Slow to avoid this.

virtual/outofblink-cors-ns/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-simple.html
virtual/outofblink-cors-ns/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-synconworker.html
virtual/outofblink-cors/http/tests/xmlhttprequest/timeout/xmlhttprequest-timeout-worker-aborted.html
virtual/threaded/fast/scrolling/overflow-scrollability.html

TBR=fdegans
NOTRY=true
Bug: 869662

Change-Id: Ib22bc7c2aaca91ee8b699e99cbd22a8d419e9fe8
Reviewed-on: https://chromium-review.googlesource.com/1157536
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579622}
[modify] https://crrev.com/5daa8048adfc79c170d639eeda8dc96eeab16fb7/third_party/WebKit/LayoutTests/SlowTests

Issue 869800 has been merged into this issue.

The bug was for mac 10.13 specific slow tests.

We are seeing slow results on outofblink-cors tests even on other bots. So, let me split it and remove CORS related flag again.

bokan@: PTAL

bokan@, this came up in https://foolip.github.io/ecosystem-infra-rotation/ today, is this something you're still working on?

It is, unfortunately we've got a really bad problem with input tests due to the highly async nature of our pipeline. Our testing infrastructure hasn't kept up with changes in the pipeline so we have a ton of flaky and slow tests like this. Unfortunately it's not possible to make these perfectly reliable and we've spent much time trying to fix tests but having them come back flaky.

I'm actively building out improved infrastructure so that we can make tests like this fast and reliable. Details are in https://docs.google.com/document/d/1B4hXTkEsvixMAB7xT1MSLlQtEEApZK5xzSMwNScQGKg/edit# if you're interested. The goal is to make it so we don't have to "guess" when a scroll/input might be finished and in that case we can make tests run faster and more reliably.

tl;dr Working on it but it'll be a while before I get to individual tests like this.

This is now timing out. Please refer to 
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=virtual%2Ffractional_scrolling_threaded%2Ffast%2Fscrolling%2Foverflow-scrollability.html

sorry, not this one, it is the fractional_scrolling_threaded one that is timing out, will file another bug.