Findit identified the culprit r576110 with confidence 70.0% in the config "chromium.chromiumos / linux-chromeos-dbg"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVywgELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKLAWNocm9taXVtLmNocm9taXVtb3MvbGludXgtY2hyb21lb3MtZGJnLzY4OTMvdW5pdF90ZXN0cy9SR1YyYVdObFRHOWpZV3hCWTJOdmRXNTBSWGgwWlhKdVlXeFFiMnhwWTNsTWIyRmtaWEpVWlhOMExrWnZjbU5sU1c1emRHRnNiRXhwYzNSVFpYUT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

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%20DeviceLocalAccountExternalPolicyLoaderTest.ForceInstallListSet&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVywgELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKLAWNocm9taXVtLmNocm9taXVtb3MvbGludXgtY2hyb21lb3MtZGJnLzY4OTMvdW5pdF90ZXN0cy9SR1YyYVdObFRHOWpZV3hCWTJOdmRXNTBSWGgwWlhKdVlXeFFiMnhwWTNsTWIyRmtaWEpVWlhOMExrWnZjbU5sU1c1emRHRnNiRXhwYzNSVFpYUT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

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

Sample failure output:

[ RUN      ] DeviceLocalAccountExternalPolicyLoaderTest.ForceInstallListSet
[11936:11936:0719/073408.149420:5832970008:ERROR:network_service.cc(66)] Not implemented reached in std::unique_ptr<net::NetworkChangeNotifier> network::(anonymous namespace)::CreateNetworkChangeNotifierIfNeeded()
../../chrome/browser/chromeos/extensions/device_local_account_external_policy_loader_unittest.cc:317: Failure
Value of: base::MessageLoopCurrent::Get()->IsIdleForTesting()
  Actual: false
Expected: true
Stack trace:
#0 0x00000476e9e0 StackTraceGetter::CurrentStackTrace()
#1 0x0000047920b7 testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#2 0x00000479151d testing::internal::AssertHelper::operator=()
#3 0x000003cfc3f7 chromeos::DeviceLocalAccountExternalPolicyLoaderTest_ForceInstallListSet_Test::TestBody()
#4 0x000002e2015e _ZN7testing8internal12InvokeHelperIN16sync_file_system18RemoteServiceStateENSt3__15tupleIJEEEE12InvokeMethodINS2_25MockRemoteFileSyncServiceEMS9_KFS3_vEEES3_PT_T0_RKS6_

ahest@yandex-team.ru: this does seem related to r576110. Can you please take a look?

I was trying to resolve this in https://chromium-review.googlesource.com/c/chromium/src/+/1120494. BTW, does it make sense to keep the bug open, taking into account that the culprit CL is reverted?

Yes, let's keep the bug opened (especially given decision there to reland with this test disabled).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/782c0e31591d55a13aa3d488357bf7bdbe174b46

commit 782c0e31591d55a13aa3d488357bf7bdbe174b46
Author: Alexander Semashko <ahest@yandex-team.ru>
Date: Wed Aug 15 12:26:49 2018

Reland #4: Switch WindowedNotificationObserver to use base::RunLoop.

Now it will quit the message loop immediately after receiving the
notification. Also it does not allow nested tasks anymore.

Flaky test DeviceLocalAccountExternalPolicyLoaderTest.ForceInstallListSet
is termporarily disabled.

TBR=jam@chromium.org

Bug: 668707, 865453 
Change-Id: I1cbceb298311a9b7905c0cec410cb82330effccd
Reviewed-on: https://chromium-review.googlesource.com/1146700
Commit-Queue: Alexander Semashko <ahest@yandex-team.ru>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Drew Wilson <atwilson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583220}
[modify] https://crrev.com/782c0e31591d55a13aa3d488357bf7bdbe174b46/chrome/browser/chromeos/extensions/device_local_account_external_policy_loader_unittest.cc
[modify] https://crrev.com/782c0e31591d55a13aa3d488357bf7bdbe174b46/content/public/test/test_utils.cc
[modify] https://crrev.com/782c0e31591d55a13aa3d488357bf7bdbe174b46/content/public/test/test_utils.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5232132f450489fb6fd6624f977503310d6032e1

commit 5232132f450489fb6fd6624f977503310d6032e1
Author: Alexander Semashko <ahest@yandex-team.ru>
Date: Tue Aug 21 09:40:42 2018

Fix and enable DeviceLocalAccountExternalPolicyLoaderTest.ForceInstallListSet.

The test was disabled because switching WindowedNotificationObserver to use
base::RunLoop instead of deprecated MessageLoopRunner made it flaky.

R=atwilson@chromium.org

Bug: 668707,  865453 
Change-Id: Ideff2420f51232bb7e590a0f242efaec64f598a0
Reviewed-on: https://chromium-review.googlesource.com/1120494
Commit-Queue: Alexander Semashko <ahest@yandex-team.ru>
Reviewed-by: Drew Wilson <atwilson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584700}
[modify] https://crrev.com/5232132f450489fb6fd6624f977503310d6032e1/chrome/browser/chromeos/extensions/device_local_account_external_policy_loader_unittest.cc