See flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=LocalNTPJavascriptTest

It's been going on for a few weeks at least, unfortunately the dashboard doesn't go further back than that.


Logs look like this:

[ RUN      ] LocalNTPJavascriptTest.SimpleJavascriptTests
[6148:3772:1116/210646.316:WARNING:chrome_browser_main_win.cc(613)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=LocalNTPJavascriptTest.SimpleJavascriptTests --single_process --test-launcher-bot-mode --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5432_27524\results5432_9566\test_results.xml" --test-launcher-summary-output="e:\b\swarm_slave\w\iogxwc3c\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5432_27524\d5432_14443" --disable-offline-auto-reload --no-first-run --no-default-browser-check --enable-logging=stderr --safebrowsing-disable-auto-update --disable-default-apps --wm-window-animations-disabled --disable-component-update --test-type=browser --force-color-profile=srgb --disable-zero-browsers-open-for-tests --ipc-connection-timeout=45 --allow-file-access-from-files --dom-automation --log-gpu-control-list-decisions --disable-backgrounding-occluded-windows --disable-gl-drawing-for-tests --override-use-software-gl-for-tests --force-color-profile=srgb --enable-features=TestFeatureForBrowserTest1,UseGoogleLocalNtp --disable-features=NetworkPrediction,TestFeatureForBrowserTest2 --flag-switches-begin --flag-switches-end --restore-last-session about:blank
[4740:7056:1116/210647.576:INFO:media_foundation_video_encode_accelerator_win.cc(370)] Windows versions earlier than 8 are not supported.
[6148:1096:1116/210651.589:WARNING:embedded_test_server.cc(228)] Request not handled. Returning 404: /favicon.ico
[6148:3772:1116/210652.047:WARNING:render_frame_host_impl.cc(2682)] OnDidStopLoading was called twice.
[6148:3772:1116/210652.095:FATAL:web_contents_observer_sanity_checker.cc(297)] Check failed: !is_loading_. 
Backtrace:
	base::debug::StackTrace::StackTrace [0x100BCED6+102]
	base::debug::StackTrace::StackTrace [0x100BBA73+35]
	logging::LogMessage::~LogMessage [0x10132665+149]
	content::WebContentsObserverSanityChecker::DidStartLoading [0x05BF4E1F+191]
	content::WebContentsImpl::LoadingStateChanged [0x1DDD022C+1340]
	content::WebContentsImpl::DidStartLoading [0x1DDDBC37+103]
	content::FrameTreeNode::DidStartLoading [0x1CD8814A+138]
	content::RenderFrameHostImpl::DidCommitProvisionalLoad [0x1CE3FA62+3474]
	content::mojom::FrameHostStubDispatch::Accept [0x1B23362D+1373]
	content::mojom::FrameHostStub<mojo::RawPtrImplRefTraits<content::mojom::FrameHost> >::Accept [0x1CE77219+89]
	mojo::InterfaceEndpointClient::HandleValidatedMessage [0x0F3C181D+1917]
	mojo::InterfaceEndpointClient::HandleIncomingMessageThunk::Accept [0x0F3C1080+32]
	mojo::FilterChain::Accept [0x0F3BF029+489]
	mojo::InterfaceEndpointClient::HandleIncomingMessage [0x0F3C4A94+260]
	std::_Compressed_pair<std::default_delete<mojo::Connector>,mojo::Connector *,1>::_Get_first [0x161F11B2+2690]
	std::_Default_allocator_traits<std::allocator<mojo::Message> >::destroy<mojo::Message> [0x161E0905+1349]
	std::_Default_allocator_traits<std::allocator<mojo::Message> >::destroy<mojo::Message> [0x161E07A1+993]
	std::_Default_allocator_traits<std::allocator<mojo::Message> >::destroy<mojo::Message> [0x161E06DC+796]
	std::_Default_allocator_traits<std::allocator<mojo::Message> >::destroy<mojo::Message> [0x161E056E+430]
	base::OnceCallback<void __cdecl(void)>::Run [0x10043C7E+78]
	base::debug::TaskAnnotator::RunTask [0x100C1925+1013]
	base::internal::IncomingTaskQueue::RunTask [0x1016DB4D+253]
	base::MessageLoop::RunTask [0x10178CAD+1005]
	base::MessageLoop::DeferOrRunPendingTask [0x10179791+81]
	base::MessageLoop::DoWork [0x10179A66+454]
	base::MessagePumpForUI::DoRunLoop [0x101863CE+62]
	base::MessagePumpWin::Run [0x10185581+193]
	base::MessageLoop::Run [0x1017837F+559]
	base::RunLoop::Run [0x1026E379+537]
	content::RunThisRunLoop [0x05A988B5+53]
	content::MessageLoopRunner::Run [0x05A99FF1+257]
	content::DOMMessageQueue::WaitForMessage [0x05AABDC1+353]
	content::ExecuteScriptAndExtractDouble [0x05AA8E9C+924]
	content::ExecuteScriptAndExtractBool [0x05AA9660+288]
	instant_test_utils::GetBoolFromJS [0x01A2DBA5+85]
	LocalNTPJavascriptTest_SimpleJavascriptTests_Test::RunTestOnMainThread [0x01A3C2DB+651]
	content::BrowserTestBase::ProxyRunTestOnMainThreadLoop [0x05AE1AFB+539]
	??$Invoke@PAVBrowserTestBase@content@@$$V@?$FunctorTraits@P8BrowserTestBase@content@@AEXXZX@internal@base@@SAXP8BrowserTestBase@content@@AEXXZ$$QAPAV34@@Z [0x05AE4C9C+28]
	base::internal::InvokeHelper<0,void>::MakeItSo<void (__thiscall content::BrowserTestBase::*const &)(void),content::BrowserTestBase *> [0x05AE4BCD+77]
	base::internal::Invoker<base::internal::BindState<void (__thiscall content::BrowserTestBase::*)(void),base::internal::UnretainedWrapper<content::BrowserTestBase> >,void __cdecl(void)>::RunImpl<void (__thiscall content::BrowserTestBase::*const &)(void),std [0x05AE4B53+83]
	base::internal::Invoker<base::internal::BindState<void (__thiscall content::BrowserTestBase::*)(void),base::internal::UnretainedWrapper<content::BrowserTestBase> >,void __cdecl(void)>::Run [0x05AE4A2E+62]
	base::RepeatingCallback<void __cdecl(void)>::Run [0x00A20F92+50]
	ChromeBrowserMainParts::PreMainMessageLoopRunImpl [0x06267620+7664]
	ChromeBrowserMainParts::PreMainMessageLoopRun [0x06265723+419]
	content::BrowserMainLoop::PreMainMessageLoopRun [0x1C763848+360]
	??$Invoke@PAVBrowserMainLoop@content@@$$V@?$FunctorTraits@P8BrowserMainLoop@content@@AEHXZX@internal@base@@SAHP8BrowserMainLoop@content@@AEHXZ$$QAPAV34@@Z [0x1C774A2C+28]
	base::internal::InvokeHelper<0,int>::MakeItSo<int (__thiscall content::BrowserMainLoop::*const &)(void),content::BrowserMainLoop *> [0x1C77494D+77]
	base::internal::Invoker<base::internal::BindState<int (__thiscall content::BrowserMainLoop::*)(void),base::internal::UnretainedWrapper<content::BrowserMainLoop> >,int __cdecl(void)>::RunImpl<int (__thiscall content::BrowserMainLoop::*const &)(void),std::t [0x1C7748D3+83]
	base::internal::Invoker<base::internal::BindState<int (__thiscall content::BrowserMainLoop::*)(void),base::internal::UnretainedWrapper<content::BrowserMainLoop> >,int __cdecl(void)>::Run [0x1C77474E+62]
	base::RepeatingCallback<int __cdecl(void)>::Run [0x1DCE1CE2+50]
	content::StartupTaskRunner::RunAllTasksNow [0x1DCE1A28+136]
	content::BrowserMainLoop::CreateStartupTasks [0x1C75FB6D+1165]
	content::BrowserMainRunnerImpl::Initialize [0x1C77FC48+1560]
	content::BrowserMain [0x1C758586+182]
	content::RunNamedProcessTypeMain [0x1FAB0E71+209]
	content::ContentMainRunnerImpl::Run [0x1FAB1EB2+658]
	content::ContentServiceManagerMainDelegate::RunEmbedderProcess [0x1FAAD701+33]
	service_manager::Main [0x22E572FE+1534]
	content::ContentMain [0x1FAB0CEA+74]
	content::BrowserTestBase::SetUp [0x05AE120A+2970]
	InProcessBrowserTest::SetUp [0x0566CB15+1557]
	LocalNTPTest::SetUp [0x01A55BF4+52]
[102/325] LocalNTPJavascriptTest.SimpleJavascriptTests (CRASHED)


So apparently RenderFrameHostImpl::OnDidStopLoading somehow gets called twice, which makes WebContentsObserverSanityChecker unhappy. I don't know how that would be caused by something in that test...