The flakiness dashboard shows this as specific to single-process-mash. Here's sample output when it fails:
[ RUN      ] PasswordManagerInteractiveTest.PromptForXHRWithoutOnSubmit
[29236:29236:1114/190116.286019:WARNING:chrome_browser_main_chromeos.cc(547)] Running as stub user with profile dir: test-user
[29236:29236:1114/190116.350113:WARNING:easy_unlock_service_regular.cc(522)] EasyUnlockServiceRegular::IsInLegacyHostMode: DeviceSyncClient not ready. Returning false.
[29236:29236:1114/190116.357718:INFO:remote_commands_service.cc(38)] Fetching remote commands.
[29236:29236:1114/190116.377361:WARNING:remote_commands_service.cc(40)] Client is not registered.
[29236:29236:1114/190116.377392:INFO:remote_commands_invalidator.cc(32)] Initialize RemoteCommandsInvalidator.
[29236:29236:1114/190116.377413:INFO:remote_commands_invalidator.cc(57)] Starting RemoteCommandsInvalidator.
[29236:29236:1114/190116.377430:INFO:remote_commands_invalidator.cc(123)] RemoteCommandsInvalidator ReloadPolicyData.
[29236:29236:1114/190116.377447:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
[29236:29236:1114/190116.389003:WARNING:wallpaper_controller_client.cc(358)] Cannot get wallpaper files id in RemovePolicyWallpaper. This should never happen under normal circumstances.
[29236:29236:1114/190116.476106:ERROR:gpu_interface_provider.cc(87)] Not implemented reached in virtual void content::GpuInterfaceProvider::RegisterOzoneGpuInterfaces(service_manager::BinderRegistry *)
[29236:29236:1114/190116.490060:ERROR:layer_tree_host_impl.cc(3157)] Forcing zero-copy tile initialization as worker context is missing
[29236:29236:1114/190116.493272:ERROR:layer_tree_host_impl.cc(3157)] Forcing zero-copy tile initialization as worker context is missing
[29236:29236:1114/190116.501622:ERROR:remote_text_input_client.cc(158)] Not implemented reached in virtual void RemoteTextInputClient::OnInputMethodChanged()
[29236:29236:1114/190116.501643:ERROR:remote_text_input_client.cc(115)] Not implemented reached in virtual ui::TextInputClient::FocusReason RemoteTextInputClient::GetFocusReason() const
[29236:29236:1114/190116.501649:ERROR:remote_text_input_client.cc(200)] Not implemented reached in virtual bool RemoteTextInputClient::ShouldDoLearning()
[29236:29236:1114/190116.501660:ERROR:remote_text_input_client.cc(109)] Not implemented reached in virtual bool RemoteTextInputClient::HasCompositionText() const
[29236:29236:1114/190116.501667:ERROR:remote_text_input_client.cc(121)] Not implemented reached in virtual bool RemoteTextInputClient::GetTextRange(gfx::Range *) const
[29236:29236:1114/190116.501671:ERROR:remote_text_input_client.cc(176)] Not implemented reached in virtual void RemoteTextInputClient::EnsureCaretNotInRect(const gfx::Rect &)
[29236:29236:1114/190116.506026:ERROR:layer_tree_host_impl.cc(3157)] Forcing zero-copy tile initialization as worker context is missing
[29236:29236:1114/190116.544114:ERROR:render_widget_host_view_aura.cc(1289)] Not implemented reached in virtual base::i18n::TextDirection content::RenderWidgetHostViewAura::GetTextDirection() const
[29236:29236:1114/190116.604756:INFO:CONSOLE(0)] "[DOM] Input elements should have autocomplete attributes (suggested: "current-password"): (More info: https://goo.gl/9p2vKq) %o", source: http://127.0.0.1:44814/password/password_xhr_submit.html (0)
[29236:29236:1114/190116.604795:INFO:CONSOLE(0)] "[DOM] Input elements should have autocomplete attributes (suggested: "username"): (More info: https://goo.gl/9p2vKq) %o", source: http://127.0.0.1:44814/password/password_xhr_submit.html (0)
[29236:29316:1114/190116.609661:WARNING:embedded_test_server.cc(239)] Request not handled. Returning 404: /favicon.ico
../../chrome/browser/password_manager/password_manager_interactive_uitest.cc:193: Failure
Value of: BubbleObserver(WebContents()).IsSavePromptShownAutomatically()
  Actual: false
Expected: true
Stack trace:
#0 0x5633ce21bc4c testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#1 0x5633ce21b629 testing::internal::AssertHelper::operator=()
#2 0x5633cdfbdc96 password_manager::PasswordManagerInteractiveTest_PromptForXHRWithoutOnSubmit_Test::RunTestOnMainThread()
#3 0x5633d0a6658b content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#4 0x5633d065bd93 ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#5 0x5633d065ace2 ChromeBrowserMainParts::PreMainMessageLoopRun()
#6 0x5633cf806897 chromeos::ChromeBrowserMainPartsChromeos::PreMainMessageLoopRun()
#7 0x5633cee63bc5 content::BrowserMainLoop::PreMainMessageLoopRun()
#8 0x5633cf1f6647 content::StartupTaskRunner::RunAllTasksNow()
#9 0x5633cee628d0 content::BrowserMainLoop::CreateStartupTasks()
#10 0x5633cee65d49 content::BrowserMainRunnerImpl::Initialize()
#11 0x5633cee60b52 content::BrowserMain()
#12 0x5633d04420bc content::ContentMainRunnerImpl::Run()
#13 0x5633d22fd3d2 service_manager::Main()
#14 0x5633d0440564 content::ContentMain()
#15 0x5633d0a661d1 content::BrowserTestBase::SetUp()
#16 0x5633d064d234 InProcessBrowserTest::SetUp()

[29236:29236:1114/190116.769685:ERROR:http_bridge.cc(126)] Not implemented reached in virtual void syncer::HttpBridgeFactory::OnSignalReceived()
[29236:29236:1114/190116.770262:INFO:remote_commands_invalidator.cc(45)] Shutdown RemoteCommandsInvalidator.
[29236:29236:1114/190116.770331:INFO:remote_commands_invalidator.cc(68)] Stopping RemoteCommandsInvalidator.
[29236:29236:1114/190116.770347:INFO:remote_commands_invalidator.cc(167)] Unregister RemoteCommandsInvalidator.
[29236:29236:1114/190116.791014:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[29236:29236:1114/190116.800391:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.