Stack trace found on https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-xenial-rel/6226:

[ RUN      ] UkmBrowserTestWithSyncTransport.NotEnabledForSecondaryAccountSync/1
[19705:19705:0109/161454.668504:44932383245:WARNING:loopback_server.cc(719)] Loopback sync persistent state file does not exist.
[19705:19705:0109/161454.900406:WARNING:password_store_factory.cc(261)] Using basic (unencrypted) store for password storage. See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_password_storage.md for more information about password storage options.

(browser_tests:19705): LIBDBUSMENU-GLIB-WARNING **: Unable to get session bus: Unknown or unsupported transport 'disabled' for address 'disabled:'
[19705:19755:0109/161455.028111:ERROR:bus.cc(396)] Failed to connect to the bus: Could not parse server address: Unknown address type (examples of valid types are "tcp" and on UNIX "unix")
../../chrome/browser/metrics/ukm_browsertest.cc:1167: Failure
Expected: (syncer::SyncService::TransportState::DISABLED) != (sync_service->GetTransportState()), actual: 4-byte object <00-00 00-00> vs 4-byte object <00-00 00-00>
Stack trace:
#0 0x5598772741ec testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#1 0x559877273bd9 testing::internal::AssertHelper::operator=()
#2 0x559876120469 metrics::UkmBrowserTestWithSyncTransport_NotEnabledForSecondaryAccountSync_Test::RunTestOnMainThread()
#3 0x559879730571 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#4 0x5598792ed616 ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#5 0x5598792ec312 ChromeBrowserMainParts::PreMainMessageLoopRun()
#6 0x559877cb5fa2 content::BrowserMainLoop::PreMainMessageLoopRun()
#7 0x559878050d77 content::StartupTaskRunner::RunAllTasksNow()
#8 0x559877cb4b7d content::BrowserMainLoop::CreateStartupTasks()
#9 0x559877cb8312 content::BrowserMainRunnerImpl::Initialize()
#10 0x559877cb2f5e content::BrowserMain()
#11 0x559878f69caa content::ContentMainRunnerImpl::RunServiceManager()
#12 0x559878f69926 content::ContentMainRunnerImpl::Run()
#13 0x55987ad02138 service_manager::Main()
#14 0x559878f67de1 content::ContentMain()
#15 0x559879730193 content::BrowserTestBase::SetUp()
#16 0x559879299db2 InProcessBrowserTest::SetUp()
#17 0x559879c00415 SyncTest::SetUp()
#18 0x55987612101f metrics::UkmBrowserTestBase::SetUp()

[19705:19705:0109/161455.422626:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[19705:19705:0109/161455.422656:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[  FAILED  ] UkmBrowserTestWithSyncTransport.NotEnabledForSecondaryAccountSync/1, where GetParam() = true (755 ms)

Forgot to update the CL description with this bug - r621200 was reverted in

https://chromium-review.googlesource.com/c/chromium/src/+/1404540

Removing sheriff label - please add it back if this revert was incorrect and there is another cause for the flaky test. Thanks!

Lowell, any progress on relanding the CL? Would you mind decreasing prio to P2? (it bumps up on our triage dashboard every week to nag on progress)

Hi Jan,

I wasn't able to reproduce the flake manually, so I opted to take a different approach for this test.

I'll mark this as fixed.

Thanks!