Seems related to test injected events.

Example:
[ RUN      ] MouseLatencyBrowserTest.CoalescedMouseWheelsCorrectlyTerminated
[157341:157357:0914/100254.579604:ERROR:network_service.cc(84)] Not implemented reached in std::unique_ptr<net::NetworkChangeNotifier> network::(anonymous namespace)::CreateNetworkChangeNotifierIfNeeded()
[157341:157341:0914/100254.666422:ERROR:gpu_interface_provider.cc(85)] Not implemented reached in virtual void content::GpuInterfaceProvider::RegisterOzoneGpuInterfaces(service_manager::BinderRegistry *)

DevTools listening on ws://127.0.0.1:41423/devtools/browser/8a9421a7-2f08-488d-b315-594d0c021f8b
[157341:157341:0914/100254.673807:ERROR:proxy_resolution_service.cc(1556)] ProxyConfigService for ChromeOS should be created in profile_io_data.cc::CreateProxyConfigService and this should be used only for examples.
[157341:157341:0914/100254.757791:ERROR:render_widget_host_view_aura.cc(1255)] Not implemented reached in virtual base::i18n::TextDirection content::RenderWidgetHostViewAura::GetTextDirection() const
[157341:157341:0914/100255.393557:ERROR:layer_tree_host_impl.cc(3060)] Forcing zero-copy tile initialization as worker context is missing
[1:8:0914/100255.416315:ERROR:layer_tree_host_impl.cc(3060)] Forcing zero-copy tile initialization as worker context is missing
[157341:157341:0914/100255.555509:FATAL:server_window.cc(328)] Check failed: !event->IsPointerEvent(). 
#0 0x7f5516de447d base::debug::StackTrace::StackTrace()
#1 0x7f5516af8c6c base::debug::StackTrace::StackTrace()
#2 0x7f5516b62bfd logging::LogMessage::~LogMessage()
#3 0x7f54f8b89093 ws::(anonymous namespace)::TopLevelEventHandler::OnEvent()
#4 0x7f550bcf878a ui::EventDispatcher::DispatchEvent()
#5 0x7f550bcf7f77 ui::EventDispatcher::DispatchEventToEventHandlers()
#6 0x7f550bcf6f8a ui::EventDispatcher::ProcessEvent()
#7 0x7f550bcf6b04 ui::EventDispatcherDelegate::DispatchEventToTarget()
#8 0x7f550bcf69f6 ui::EventDispatcherDelegate::DispatchEvent()
#9 0x7f550bcfc0f8 ui::EventProcessor::OnEventFromSource()
#10 0x7f550bcfc3cc ui::EventProcessor::OnEventFromSource()
#11 0x7f54f8b72440 ws::EventInjector::InjectEventNoAck()
#12 0x7f54f8c06255 ws::mojom::EventInjectorStubDispatch::Accept()
#13 0x7f54f8b75453 ws::mojom::EventInjectorStub<>::Accept()
#14 0x7f551a7d8465 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#15 0x7f551a7d6f21 mojo::InterfaceEndpointClient::HandleIncomingMessageThunk::Accept()
#16 0x7f551a7d53d8 mojo::FilterChain::Accept()
#17 0x7f551a7dadf6 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#18 0x7f551a7e7412 mojo::internal::MultiplexRouter::ProcessIncomingMessage()
#19 0x7f551a7e6a35 mojo::internal::MultiplexRouter::Accept()
#20 0x7f551a7d53d8 mojo::FilterChain::Accept()
#21 0x7f551a7c7fb2 mojo::Connector::ReadSingleMessage()
#22 0x7f551a7c8f3a mojo::Connector::ReadAllAvailableMessages()