Findit identified the culprit r565169 with confidence 86.2% in the config "chromium.chromiumos / linux-chromeos-rel"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyrQELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJ3Y2hyb21pdW0uY2hyb21pdW1vcy9saW51eC1jaHJvbWVvcy1yZWwvOTEzMC9tYXNoX2Jyb3dzZXJfdGVzdHMvVTJoMWRHUnZkMjVRYjJ4cFkzbEpibE5sYzNOcGIyNVVaWE4wTGxCdmJHbGplVU5vWVc1blpRPT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA


Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).
Feedback is welcome! Please use component Tools>Test>FindIt>Flakiness

For convenience, link to flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=mash_browser_tests&tests=ShutdownPolicyInSessionTest.PolicyChange

Because the patch introducing the flake was introduced last Thursday and there are likely dependencies on it (at least according to gerrit), I'm sending out  https://chromium-review.googlesource.com/#/c/chromium/src/+/1095186
to disable the test.

assigning to tetsui@, the author of the breaking patch.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/be6c791b8c7d9d455e9c3bef61074f5e83646bdb

commit be6c791b8c7d9d455e9c3bef61074f5e83646bdb
Author: Tim Schumann <tschumann@chromium.org>
Date: Mon Jun 11 11:06:50 2018

Disable flaky test ShutdownPolicyInSessionTest.PolicyChange

TBR=tetsui@chromium.org

Bug:  851208 , 847104 
Change-Id: Iaec639e8b79485f711967f67e439c3f1fe205d93
Reviewed-on: https://chromium-review.googlesource.com/1095186
Reviewed-by: Tim Schumann <tschumann@chromium.org>
Commit-Queue: Tim Schumann <tschumann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565960}
[modify] https://crrev.com/be6c791b8c7d9d455e9c3bef61074f5e83646bdb/chrome/browser/chromeos/shutdown_policy_browsertest.cc