Findit identified the culprit r579950 with confidence 70.0% in the config "chromium.mac / Mac10.13 Tests"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJxY2hyb21pdW0ubWFjL01hYzEwLjEzIFRlc3RzLzQ1MjEvdmlld3NfdW5pdHRlc3RzL1RtRjBhWFpsVjJsa1oyVjBUV0ZqVkdWemRDNVRZMmhsWkhWc1pWQmhhVzUwU1c1U1pXTjBYMVJwZEd4bFpBPT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20NativeWidgetMacTest.SchedulePaintInRect_Titled&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJxY2hyb21pdW0ubWFjL01hYzEwLjEzIFRlc3RzLzQ1MjEvdmlld3NfdW5pdHRlc3RzL1RtRjBhWFpsVjJsa1oyVjBUV0ZqVkdWemRDNVRZMmhsWkhWc1pWQmhhVzUwU1c1U1pXTjBYMVJwZEd4bFpBPT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

sugoi@ Looks like there is another test that has started flaking since your CL. Could you disable it?

Looking at the bots, this flakiness only caused a single failure so far on build 4521. I'll try to find a proper fix tomorrow before disabling it, and the failure only happens in a subsection of the test, so I could disable only part of it if I can't find a proper fix. It looks like a synchronization issue at first glance.

NativeWidgetMacTest.SchedulePaintInRect_Borderless is flaking too, probably for the same reason.

NativeWidgetMacTest.SchedulePaintInRect_Titled
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.13%20Tests/4521
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests/14743

NativeWidgetMacTest.SchedulePaintInRect_Borderless
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests/14744
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests/14741
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests/14737
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests/14733

 Issue 870421  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/85cdc133a47282d9c630fcd95bd1c1c6c5313382

commit 85cdc133a47282d9c630fcd95bd1c1c6c5313382
Author: Alexis Hetu <sugoi@google.com>
Date: Fri Aug 03 19:11:19 2018

NativeWidgetMacTest.SchedulePaintInRect_* fix

The gl renderer for all chromium tests was recently changed from OSMesa
to SwiftShader. OSMesa offers a synchronous API to OpenGL, while
SwiftShader is asynchronous (draw calls are received and yield before
the drawing operation is complete, letting chromium resume its execution).

Because of this it seems like the affected MacOS tests here can become
idle while rendering is happening in the background, causing the tests to
fail. To solve this, we need to actually wait for drawing to be completed,
rather than waiting for an idle period, in order to resume the test. Doing
this allows these tests to pass.

R=ccameron@chromium.org

Bug:  chromium:870465 
Change-Id: I6f1555b93a83d80b06e72b3a469c01dde44e1312
Reviewed-on: https://chromium-review.googlesource.com/1162350
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580619}
[modify] https://crrev.com/85cdc133a47282d9c630fcd95bd1c1c6c5313382/ui/views/widget/native_widget_mac_unittest.mm