Example failure log (from https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.chromiumos%2FLinux_ChromiumOS_Tests__1_%2F43616%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests%2F0%2Flogs%2FProfileManagerBrowserTest.EphemeralProfile%2F0): 

../../chrome/browser/profiles/profile_manager_browsertest.cc:552: Failure
      Expected: path_profile1
      Which is: /b/s/w/itvtYX7b/.org.chromium.Chromium.cRZHuJ/dp4NSlv/LockScreenAppsProfile
To be equal to: browser_list->get(0)->profile()->GetPath()
      Which is: /b/s/w/itvtYX7b/.org.chromium.Chromium.cRZHuJ/dp4NSlv/test-user

Lock screen apps seem to be a relatively recent thing -- Toni, could you take a look?

Tim, do you have a link to ProfileManagerBrowserTest.SwitchToProfile failing? I can't find one on https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29.

(In general it's a good idea to link to the exact failures -- the more time passes, the more difficult it will be to dig them out later. It's also useful to post the actual error messages in the bug, so they will show up if someone searches for them.)

Sure, here you go:

Failure of the EphemeralProfile test:
build: https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/43616
[ RUN      ] ProfileManagerBrowserTest.EphemeralProfile
[28432:28432:0825/033703.932145:WARNING:chrome_browser_main_chromeos.cc(546)] Running as stub user with profile dir: test-user
[28432:28577:0825/033704.302556:WARNING:freezer_cgroup_process_manager.cc(62)] Cgroup freezer does not exist or is not writable. Unable to freeze renderer processes.
[28432:28432:0825/033704.370133:ERROR:device_event_log_impl.cc(156)] [03:37:04.370] Network: network_device_handler_impl.cc:608 Failed to determine if device /device/wifi1 supports MAC address randomization
[28432:28432:0825/033704.370164:ERROR:device_event_log_impl.cc(156)] [03:37:04.370] Network: network_handler_callbacks.cc:84 Failed to determine if device supports MAC address randomization: /device/wifi1: Missing MACAddressRandomizationSupported
../../chrome/browser/profiles/profile_manager_browsertest.cc:552: Failure
      Expected: path_profile1
      Which is: /b/s/w/itvtYX7b/.org.chromium.Chromium.cRZHuJ/dLsHtHH/LockScreenAppsProfile
To be equal to: browser_list->get(0)->profile()->GetPath()
      Which is: /b/s/w/itvtYX7b/.org.chromium.Chromium.cRZHuJ/dLsHtHH/test-user
[28432:28432:0825/033704.541789:INFO:chrome_cryptauth_service.cc(222)] Profile is not authenticated yet; waiting before starting CryptAuth managers.
[28432:28432:0825/033704.555733:INFO:chrome_cryptauth_service.cc(230)] Refresh token not yet available; waiting before starting CryptAuth managers.
[  FAILED  ] ProfileManagerBrowserTest.EphemeralProfile, where TypeParam =  and GetParam() =  (770 ms)
[283/1678] ProfileManagerBrowserTest.EphemeralProfile (1052 ms)



SwitchToProfile test. Here are two builds, both time, it crashed.

https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/43618
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/43617


[ RUN      ] ProfileManagerBrowserTest.SwitchToProfile
[25909:25909:0825/042019.419482:WARNING:chrome_browser_main_chromeos.cc(546)] Running as stub user with profile dir: test-user
[25909:25909:0825/042019.640626:WARNING:statistics_provider.cc(288)] Statistics loaded after waiting 1ms.
[25909:26063:0825/042019.780783:WARNING:freezer_cgroup_process_manager.cc(62)] Cgroup freezer does not exist or is not writable. Unable to freeze renderer processes.
[25909:25909:0825/042019.870747:ERROR:device_event_log_impl.cc(156)] [04:20:19.870] Network: network_device_handler_impl.cc:608 Failed to determine if device /device/wifi1 supports MAC address randomization
[25909:25909:0825/042019.870777:ERROR:device_event_log_impl.cc(156)] [04:20:19.870] Network: network_handler_callbacks.cc:84 Failed to determine if device supports MAC address randomization: /device/wifi1: Missing MACAddressRandomizationSupported
BrowserTestBase received signal: Segmentation fault. Backtrace:
#0 0x000002ebdbac base::debug::StackTrace::StackTrace()
#1 0x0000033ab128 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7fb5adf18cb0 <unknown>
#3 0x0000017ba1f5 chromeos::Preferences::ApplyPreferences()
#4 0x0000017ba022 chromeos::Preferences::Init()
#5 0x0000017cfb89 chromeos::ProfileHelper::ProfileStartup()
#6 0x0000054659d4 StartupBrowserCreator::LaunchBrowser()
#7 0x000003184c15 profiles::OpenBrowserWindowForProfile()
#8 0x00000318545f _ZN4base8internal7InvokerINS0_9BindStateIPFvNS_8CallbackIFvP7ProfileNS4_12CreateStatusEELNS0_8CopyModeE1ELNS0_10RepeatModeE1EEEbbS5_S6_EJSA_bbEEES7_E3RunEPNS0_13BindStateBaseEOS5_OS6_
#9 0x0000030a65d1 ProfileManager::CreateProfileAsync()
#10 0x000003184d1f profiles::SwitchToProfile()
#11 0x0000009a7317 ProfileManagerBrowserTest_SwitchToProfile_Test::RunTestOnMainThread()
#12 0x0000033aaea1 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#13 0x000002fbbffe ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#14 0x000002fbaffd ChromeBrowserMainParts::PreMainMessageLoopRun()
#15 0x0000016181ef chromeos::ChromeBrowserMainPartsChromeos::PreMainMessageLoopRun()
#16 0x000001ec10e1 content::BrowserMainLoop::PreMainMessageLoopRun()
#17 0x0000021d7db7 content::StartupTaskRunner::RunAllTasksNow()
#18 0x000001ebf76c content::BrowserMainLoop::CreateStartupTasks()
#19 0x000001ec36c0 content::BrowserMainRunnerImpl::Initialize()
#20 0x000001ebcfd7 content::BrowserMain()
#21 0x000002e724b0 content::ContentMainRunnerImpl::Run()
#22 0x00000489a9b3 service_manager::Main()
#23 0x000002e71044 content::ContentMain()
#24 0x0000033aab97 content::BrowserTestBase::SetUp()
#25 0x000002f8192c InProcessBrowserTest::SetUp()
#26 0x0000018f8da1 testing::Test::Run()
#27 0x0000018f9880 testing::TestInfo::Run()
#28 0x0000018f9d67 testing::TestCase::Run()
#29 0x000001900217 testing::internal::UnitTestImpl::RunAllTests()
#30 0x0000018ffe97 testing::UnitTest::Run()
#31 0x000002f95b2e base::TestSuite::Run()
#32 0x000002eb2779 ChromeTestSuiteRunner::RunTestSuite()
#33 0x0000033d87cc content::LaunchTests()
#34 0x000002eb2b41 LaunchChromeTests()
#35 0x000002eb025b main
#36 0x7fb5adf03f45 __libc_start_main
#37 0x000000595833 <unknown>

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d924a57512548bf279d9c5879b9baefe6c0f0e5f

commit d924a57512548bf279d9c5879b9baefe6c0f0e5f
Author: Tim Schumann <tschumann@chromium.org>
Date: Fri Aug 25 12:52:54 2017

Disable ProfileManagerBrowserTest.SwitchToProfile and EphemeralProfile

TBR=bauerb@chromium.org

Bug:  758930 
Change-Id: Iec85e3917fc01553d273f14f6c4e56be7832733c
Reviewed-on: https://chromium-review.googlesource.com/635584
Commit-Queue: Tim Schumann <tschumann@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Tim Schumann <tschumann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497382}
[modify] https://crrev.com/d924a57512548bf279d9c5879b9baefe6c0f0e5f/chrome/browser/profiles/profile_manager_browsertest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b43cf014d9ccb7ac6a444377f8821d58f8769430

commit b43cf014d9ccb7ac6a444377f8821d58f8769430
Author: Francois Doray <fdoray@chromium.org>
Date: Fri Aug 25 17:14:44 2017

Disable ProfileManagerBrowserTest.SwitchToProfile and EphemeralProfile correctly.

https://chromium-review.googlesource.com/c/chromium/src/+/635584 used
DISABLE instead of DISABLED.

TBR=bauerb@chromium.org

Bug:  758930 
Change-Id: I53e602b89dc84d51d4e91ff42d924f5175d6f152
Reviewed-on: https://chromium-review.googlesource.com/635609
Reviewed-by: Francois Doray <fdoray@chromium.org>
Commit-Queue: Francois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497445}
[modify] https://crrev.com/b43cf014d9ccb7ac6a444377f8821d58f8769430/chrome/browser/profiles/profile_manager_browsertest.cc

Removing the sheriff label since these have been disabled.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d7ac011a3e294185fb5b54d5c5013d18e65ea9f8

commit d7ac011a3e294185fb5b54d5c5013d18e65ea9f8
Author: Toni Barzic <tbarzic@google.com>
Date: Tue Sep 12 18:23:55 2017

Fix ProfileManagerBrowserTests flakiness on Chrome OS

When searching for a test (user) profile, the test sin question
would search for the first non signin profile on Chrome OS. In
addition to sign-in profile, the tests should ignore lock screen apps
profile as well (userless profile recently introduced to Chrome OS,
which is used to run lock screen apps).

BUG= 758930 

Change-Id: I61ae2da9513d80a598b5fc0f6e28cf90abe81c18
Reviewed-on: https://chromium-review.googlesource.com/661147
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501338}
[modify] https://crrev.com/d7ac011a3e294185fb5b54d5c5013d18e65ea9f8/chrome/browser/profiles/profile_manager_browsertest.cc