In several builds, 
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-chromeos-rel/17843
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-chromeos-rel/17850
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-chromeos-rel/17858
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-chromeos-rel/17864


MigrationTwoClientTest.MigratePrefsAndBookmarksThenModifyBookmark
MigrationTwoClientTest.MigratePrefsThenModifyBookmark

are flaky.

Please fix those tests or disable them until there is a solution, in order to not trip the commit queue and make the Sheriff's life easier - thank you!

Stacktrace example:

[ RUN      ] MigrationTwoClientTest.MigratePrefsAndBookmarksThenModifyBookmark
Sync HTTP server started at 127.0.0.1:43469/chromiumsync...
Fake OAuth2 Token server started at 127.0.0.1:43469/o/oauth2/token...
Sync XMPP server started at 127.0.0.1:46114...
sending server_data: {"xmpp_port": 46114, "host": "127.0.0.1", "port": 43469} (56 bytes)
[1:1:1228/032156.338965:INFO:hugepage_text.cc(68)] Mlocking text pages failed: Cannot allocate memory (12)
[4377:4377:1228/032156.367356:WARNING:chrome_browser_main_chromeos.cc(544)] Running as stub user with profile dir: test-user
[4377:4377:1228/032156.419824:WARNING:easy_unlock_service_regular.cc(438)] EasyUnlockServiceRegular::IsInLegacyHostMode: DeviceSyncClient not ready. Returning false.
[4377:4377:1228/032156.431238:INFO:remote_commands_service.cc(38)] Fetching remote commands.
[4377:4377:1228/032156.449556:WARNING:remote_commands_service.cc(40)] Client is not registered.
[4377:4377:1228/032156.449628:INFO:remote_commands_invalidator.cc(32)] Initialize RemoteCommandsInvalidator.
[4377:4377:1228/032156.449668:INFO:remote_commands_invalidator.cc(57)] Starting RemoteCommandsInvalidator.
[4377:4377:1228/032156.449715:INFO:remote_commands_invalidator.cc(123)] RemoteCommandsInvalidator ReloadPolicyData.
[4377:4377:1228/032156.449802:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
[4377:4377:1228/032156.468886:WARNING:wallpaper_controller_client.cc(358)] Cannot get wallpaper files id in RemovePolicyWallpaper. This should never happen under normal circumstances.
[4377:4377:1228/032156.582779:ERROR:gpu_interface_provider.cc(87)] Not implemented reached in virtual void content::GpuInterfaceProvider::RegisterOzoneGpuInterfaces(service_manager::BinderRegistry *)
[4377:4377:1228/032156.610797:WARNING:easy_unlock_service_regular.cc(438)] EasyUnlockServiceRegular::IsInLegacyHostMode: DeviceSyncClient not ready. Returning false.
[4377:4377:1228/032156.621362:INFO:remote_commands_service.cc(38)] Fetching remote commands.
[4377:4377:1228/032156.621454:WARNING:remote_commands_service.cc(40)] Client is not registered.
[4377:4377:1228/032156.621480:INFO:remote_commands_invalidator.cc(32)] Initialize RemoteCommandsInvalidator.
[4377:4377:1228/032156.621541:INFO:remote_commands_invalidator.cc(57)] Starting RemoteCommandsInvalidator.
[4377:4377:1228/032156.621573:INFO:remote_commands_invalidator.cc(123)] RemoteCommandsInvalidator ReloadPolicyData.
[4377:4377:1228/032156.621610:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
Starting connection to 127.0.0.1:34198
Handshake done for user@gmail.com/127.0.0.1:34198.chrome-sync
[4377:4377:1228/032156.669884:WARNING:easy_unlock_service_regular.cc(438)] EasyUnlockServiceRegular::IsInLegacyHostMode: DeviceSyncClient not ready. Returning false.
[4377:4377:1228/032156.681386:INFO:remote_commands_service.cc(38)] Fetching remote commands.
[4377:4377:1228/032156.681453:WARNING:remote_commands_service.cc(40)] Client is not registered.
[4377:4377:1228/032156.681473:INFO:remote_commands_invalidator.cc(32)] Initialize RemoteCommandsInvalidator.
[4377:4377:1228/032156.681487:INFO:remote_commands_invalidator.cc(57)] Starting RemoteCommandsInvalidator.
[4377:4377:1228/032156.681504:INFO:remote_commands_invalidator.cc(123)] RemoteCommandsInvalidator ReloadPolicyData.
[4377:4377:1228/032156.681526:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
Starting connection to 127.0.0.1:34200
[4377:4377:1228/032156.718874:WARNING:easy_unlock_service_regular.cc(438)] EasyUnlockServiceRegular::IsInLegacyHostMode: DeviceSyncClient not ready. Returning false.
Handshake done for user@gmail.com/127.0.0.1:34200.chrome-sync
[4377:4377:1228/032156.728256:INFO:remote_commands_service.cc(38)] Fetching remote commands.
[4377:4377:1228/032156.728322:WARNING:remote_commands_service.cc(40)] Client is not registered.
[4377:4377:1228/032156.728350:INFO:remote_commands_invalidator.cc(32)] Initialize RemoteCommandsInvalidator.
[4377:4377:1228/032156.728370:INFO:remote_commands_invalidator.cc(57)] Starting RemoteCommandsInvalidator.
[4377:4377:1228/032156.728398:INFO:remote_commands_invalidator.cc(123)] RemoteCommandsInvalidator ReloadPolicyData.
[4377:4377:1228/032156.728423:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
[Client A -> chromiumsync.py] GetUpdates NEW_CLIENT <experiments+nigori>@0
Creating permanent item: Experiments
Creating permanent item: Nigori
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client A <- chromiumsync.py] 2 update(s)
[4377:4620:1228/032156.784531:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[4377:4620:1228/032156.785134:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[4377:4377:1228/032156.787553:ERROR:chrome_device_id_helper.cc(42)] Device ID is not set for user.
[Client A -> chromiumsync.py] GetUpdates NEW_CLIENT <device_info+priority_preference>@0, <nigori>@2
Creating permanent item: Device Info
Creating permanent item: Priority Preferences
[Client A <- chromiumsync.py] 2 update(s)
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
[4377:4377:1228/032156.796805:ERROR:account_tracker.cc(263)] OnOAuthError
[4377:4377:1228/032156.796822:WARNING:account_tracker.cc(189)] Failed to get UserInfo for user@gmail.com
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
[Client A -> chromiumsync.py] GetUpdates NEW_CLIENT <all except app_notification+article+device_info+experiments+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+nigori+priority_preference+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@0, <nigori>@4
Creating permanent item: Apps
Creating permanent item: App List
Creating permanent item: App Settings
Creating permanent item: Arc Package
Creating permanent item: Bookmarks
Creating permanent item: Bookmark Bar
Creating permanent item: Other Bookmarks
Creating permanent item: Autofill
Creating permanent item: Autofill Profiles
Creating permanent item: Autofill Wallet Items
Creating permanent item: Autofill Wallet Metadata
Creating permanent item: Extension Settings
Creating permanent item: Extensions
Creating permanent item: History Delete Directives
Creating permanent item: Favicon Images
Creating permanent item: Favicon Tracking
Creating permanent item: Passwords
Creating permanent item: Preferences
Creating permanent item: Search Engines
Creating permanent item: Sessions
Creating permanent item: Themes
Creating permanent item: Typed URLs
Creating permanent item: Dictionary
Creating permanent item: Synced Bookmarks
[Client A <- chromiumsync.py] 24 update(s)
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <experiments>@2, <device_info+priority_preference>@4, <all except app_notification+article+device_info+experiments+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+priority_preference+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@28
[Client A <- chromiumsync.py] 0 update(s)
[Client B -> chromiumsync.py] GetUpdates NEW_CLIENT <experiments+nigori>@0
[4377:4377:1228/032156.844088:ERROR:account_tracker.cc(263)] OnOAuthError
[4377:4377:1228/032156.844103:WARNING:account_tracker.cc(189)] Failed to get UserInfo for user@gmail.com
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client B <- chromiumsync.py] 2 update(s)
[4377:4621:1228/032156.847391:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[4377:4621:1228/032156.847845:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[Client A -> chromiumsync.py] Commit 25 item(s)
[4377:4377:1228/032156.851788:ERROR:chrome_device_id_helper.cc(42)] Device ID is not set for user.
[Client B -> chromiumsync.py] GetUpdates NEW_CLIENT <device_info+priority_preference>@0, <nigori>@28
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client B <- chromiumsync.py] 4 update(s)
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@28
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client A <- chromiumsync.py] 25 update(s)
[Client B -> chromiumsync.py] GetUpdates NEW_CLIENT <all except app_notification+article+device_info+experiments+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+nigori+priority_preference+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@0, <nigori>@53
[Client B <- chromiumsync.py] 47 update(s)
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
[Client B -> chromiumsync.py] GetUpdates GU_TRIGGER <experiments>@28, <all except app_notification+article+experiments+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@53
[Client B <- chromiumsync.py] 0 update(s)
[Client B -> chromiumsync.py] Commit 3 item(s)
Sending notification to user@gmail.com/127.0.0.1:34198.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34200.chrome-sync
[Client B -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@53
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client B <- chromiumsync.py] 3 update(s)
Closing connection to user@gmail.com/127.0.0.1:34198.chrome-sync
Closing connection to user@gmail.com/127.0.0.1:34200.chrome-sync
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@53
Returning encryption keys: ['4DQZEFIJJSWO02NV']
[Client A <- chromiumsync.py] 3 update(s)
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@56
[Client A <- chromiumsync.py] 0 update(s)
[Client A -> chromiumsync.py] Commit 1 item(s)
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@56
[Client A <- chromiumsync.py] 1 update(s)
Starting connection to 127.0.0.1:34276
Handshake done for user@gmail.com/127.0.0.1:34276.chrome-sync
Sending notification to user@gmail.com/127.0.0.1:34276.chrome-sync
[Client A -> chromiumsync.py] GetUpdates GU_TRIGGER <all except app_notification+article+managed_user+managed_user_setting+managed_user_shared_setting+managed_user_whitelist+reading_list+synced_notification+synced_notification_app_info+wifi_credential>@57
[Client A <- chromiumsync.py] 0 update(s)
[4377:4555:1228/032158.808713:ERROR:mcs_client.cc(709)] Failed to log in to GCM, resetting connection.
[4377:4555:1228/032158.904645:ERROR:mcs_client.cc(709)] Failed to log in to GCM, resetting connection.
Starting connection to 127.0.0.1:34382
Handshake done for user@gmail.com/127.0.0.1:34382.chrome-sync
BrowserTestBase received signal: Terminated. Backtrace:
#0 0x5630e444693f base::debug::StackTrace::StackTrace()
#1 0x5630e8131062 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7f7ccd332cb0 <unknown>
#3 0x7f7ccd3fa6d3 epoll_wait
#4 0x5630e4475fdd epoll_dispatch
#5 0x5630e4473a9c event_base_loop
#6 0x5630e445864d base::MessagePumpLibevent::Run()
#7 0x5630e43ec445 base::RunLoop::Run()
#8 0x5630e428b19f StatusChangeChecker::StartBlockingWait()
#9 0x5630e428b0bb StatusChangeChecker::Wait()
#10 0x5630e4285fd0 ProfileSyncServiceHarness::AwaitQuiescence()
#11 0x5630e4285e9b ProfileSyncServiceHarness::AwaitMutualSyncCycleCompletion()
#12 0x5630e1b4d76e (anonymous namespace)::MigrationTwoClientTest::VerifyPrefSync()
#13 0x5630e1b4d623 (anonymous namespace)::MigrationTwoClientTest::RunTwoClientMigrationTest()
#14 0x5630e1b4d9c0 (anonymous namespace)::MigrationTwoClientTest_MigratePrefsAndBookmarksThenModifyBookmark_Test::RunTestOnMainThread()
#15 0x5630e81306df content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#16 0x5630e46789ce ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#17 0x5630e46779a2 ChromeBrowserMainParts::PreMainMessageLoopRun()
#18 0x5630e33d86a2 chromeos::ChromeBrowserMainPartsChromeos::PreMainMessageLoopRun()
#19 0x5630e29ff152 content::BrowserMainLoop::PreMainMessageLoopRun()
#20 0x5630e2d8c6d7 content::StartupTaskRunner::RunAllTasksNow()
#21 0x5630e29fdf4d content::BrowserMainLoop::CreateStartupTasks()
#22 0x5630e2a01042 content::BrowserMainRunnerImpl::Initialize()
#23 0x5630e29fc45e content::BrowserMain()
#24 0x5630e406a61a content::ContentMainRunnerImpl::RunServiceManager()
#25 0x5630e406a296 content::ContentMainRunnerImpl::Run()
#26 0x5630e5e6886d service_manager::Main()
#27 0x5630e40689b4 content::ContentMain()
#28 0x5630e81301f7 content::BrowserTestBase::SetUp()
#29 0x5630e42a3866 InProcessBrowserTest::SetUp()
#30 0x5630e4291858 SyncTest::SetUp()
#31 0x5630e1d629f0 testing::Test::Run()
#32 0x5630e1d636af testing::TestInfo::Run()
#33 0x5630e1d63c07 testing::TestCase::Run()
#34 0x5630e1d6f4b7 testing::internal::UnitTestImpl::RunAllTests()
#35 0x5630e1d6f037 testing::UnitTest::Run()
#36 0x5630e43a7199 base::TestSuite::Run()
#37 0x5630e42a288d ChromeTestSuiteRunner::RunTestSuite()
#38 0x5630e813519c content::LaunchTests()
#39 0x5630e42a2d32 LaunchChromeTests()
#40 0x5630e426e4ae main
#41 0x7f7ccd31df45 __libc_start_main
#42 0x5630e1b43c4a _start
Closing connection to user@gmail.com/127.0.0.1:34382.chrome-sync
Closing connection to user@gmail.com/127.0.0.1:34276.chrome-sync