https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Debug%20%28NVIDIA%29/5097
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Debug%20%28NVIDIA%29/5113
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Debug%20%28NVIDIA%29/5116

I suspect the timeout is caused by this CHECK in ui::Compositor::DidFailToInitializeLayerTreeFrameSink():

[24871:775:0108/062124.532231:FATAL:compositor.cc(570)] Check failed: false. 
0   libbase.dylib                       0x0000000112b4b693 base::debug::StackTrace::StackTrace(unsigned long) + 83
1   libbase.dylib                       0x0000000112b4b74d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   libbase.dylib                       0x00000001128343aa base::debug::StackTrace::StackTrace() + 26
3   libbase.dylib                       0x000000011287a38e logging::LogMessage::~LogMessage() + 142
4   libbase.dylib                       0x0000000112879185 logging::LogMessage::~LogMessage() + 21
5   libcompositor.dylib                 0x0000000171ab23d3 ui::Compositor::DidFailToInitializeLayerTreeFrameSink() + 115
6   libcc.dylib                         0x000000015af03d16 cc::LayerTreeHost::DidFailToInitializeLayerTreeFrameSink() + 294
7   libcc.dylib                         0x000000015b0334de cc::SingleThreadProxy::SetLayerTreeFrameSink(cc::LayerTreeFrameSink*) + 702
8   libcc.dylib                         0x000000015af03652 cc::LayerTreeHost::SetLayerTreeFrameSink(std::__1::unique_ptr<cc::LayerTreeFrameSink, std::__1::default_delete<cc::LayerTreeFrameSink> >) + 658
9   libcompositor.dylib                 0x0000000171aaf172 ui::Compositor::SetLayerTreeFrameSink(std::__1::unique_ptr<cc::LayerTreeFrameSink, std::__1::default_delete<cc::LayerTreeFrameSink> >) + 98
10  libcontent.dylib                    0x00000001439952ba ui::HostContextFactoryPrivate::ConfigureCompositor(ui::Compositor*, scoped_refptr<viz::ContextProvider>, scoped_refptr<viz::RasterContextProvider>) + 1850
11  libcontent.dylib                    0x000000014300a18f content::VizProcessTransportFactory::OnEstablishedGpuChannel(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>) + 639
12  libcontent.dylib                    0x000000014300e332 void base::internal::FunctorTraits<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), void>::Invoke<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost> >(void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>&&, base::WeakPtr<ui::Compositor>&&, scoped_refptr<gpu::GpuChannelHost>&&) + 210
13  libcontent.dylib                    0x000000014300e1d4 void base::internal::InvokeHelper<true, void>::MakeItSo<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost> >(void (content::VizProcessTransportFactory::*&&)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>&&, base::WeakPtr<ui::Compositor>&&, scoped_refptr<gpu::GpuChannelHost>&&) + 148
14  libcontent.dylib                    0x000000014300e118 void base::internal::Invoker<base::internal::BindState<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor> >, void (scoped_refptr<gpu::GpuChannelHost>)>::RunImpl<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), std::__1::tuple<base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor> >, 0ul, 1ul>(void (content::VizProcessTransportFactory::*&&)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), std::__1::tuple<base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor> >&&, std::__1::integer_sequence<unsigned long, 0ul, 1ul>, scoped_refptr<gpu::GpuChannelHost>&&) + 120
15  libcontent.dylib                    0x000000014300e009 base::internal::Invoker<base::internal::BindState<void (content::VizProcessTransportFactory::*)(base::WeakPtr<ui::Compositor>, scoped_refptr<gpu::GpuChannelHost>), base::WeakPtr<content::VizProcessTransportFactory>, base::WeakPtr<ui::Compositor> >, void (scoped_refptr<gpu::GpuChannelHost>)>::RunOnce(base::internal::BindStateBase*, scoped_refptr<gpu::GpuChannelHost>&&) + 89
16  libcontent.dylib                    0x0000000142126be1 base::OnceCallback<void (scoped_refptr<gpu::GpuChannelHost>)>::Run(scoped_refptr<gpu::GpuChannelHost>) + 113
17  libcontent.dylib                    0x0000000142127f55 content::BrowserGpuChannelHostFactory::EstablishGpuChannel(base::OnceCallback<void (scoped_refptr<gpu::GpuChannelHost>)>) + 741
18  libcontent.dylib                    0x0000000143009ed4 content::VizProcessTransportFactory::CreateLayerTreeFrameSink(base::WeakPtr<ui::Compositor>) + 276
19  libcompositor.dylib                 0x0000000171ab231e ui::Compositor::RequestNewLayerTreeFrameSink() + 270
20  libcc.dylib                         0x000000015af03aba cc::LayerTreeHost::RequestNewLayerTreeFrameSink() + 26
21  libcc.dylib                         0x000000015b033089 cc::SingleThreadProxy::RequestNewLayerTreeFrameSink() + 249
22  libcc.dylib                         0x000000015b039fdf void base::internal::FunctorTraits<void (cc::SingleThreadProxy::*)(), void>::Invoke<void (cc::SingleThreadProxy::*)(), base::WeakPtr<cc::SingleThreadProxy> const&>(void (cc::SingleThreadProxy::*)(), base::WeakPtr<cc::SingleThreadProxy> const&&&) + 127
23  libcc.dylib                         0x000000015b039eba void base::internal::InvokeHelper<true, void>::MakeItSo<void (cc::SingleThreadProxy::* const&)(), base::WeakPtr<cc::SingleThreadProxy> const&>(void (cc::SingleThreadProxy::* const&&&)(), base::WeakPtr<cc::SingleThreadProxy> const&&&) + 106
24  libcc.dylib                         0x000000015b039e42 void base::internal::Invoker<base::internal::BindState<void (cc::SingleThreadProxy::*)(), base::WeakPtr<cc::SingleThreadProxy> >, void ()>::RunImpl<void (cc::SingleThreadProxy::* const&)(), std::__1::tuple<base::WeakPtr<cc::SingleThreadProxy> > const&, 0ul>(void (cc::SingleThreadProxy::* const&&&)(), std::__1::tuple<base::WeakPtr<cc::SingleThreadProxy> > const&&&, std::__1::integer_sequence<unsigned long, 0ul>) + 66
25  libcc.dylib                         0x000000015b039d7c base::internal::Invoker<base::internal::BindState<void (cc::SingleThreadProxy::*)(), base::WeakPtr<cc::SingleThreadProxy> >, void ()>::Run(base::internal::BindStateBase*) + 44
26  libcc.dylib                         0x000000015ad0a2bd base::RepeatingCallback<void ()>::Run() const & + 61
27  libcc.dylib                         0x000000015ad0a155 void base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::ForwardRepeating<>() + 21
28  libcc.dylib                         0x000000015ad0a57f void base::internal::FunctorTraits<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::*)(), void>::Invoke<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::*)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > const&>(void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::*)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > const&&&) + 127
29  libcc.dylib                         0x000000015ad0a45a void base::internal::InvokeHelper<true, void>::MakeItSo<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::* const&)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > const&>(void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::* const&&&)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > const&&&) + 106
30  libcc.dylib                         0x000000015ad0a3e2 void base::internal::Invoker<base::internal::BindState<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::*)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > >, void ()>::RunImpl<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::* const&)(), std::__1::tuple<base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > > const&, 0ul>(void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::* const&&&)(), std::__1::tuple<base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > > const&&&, std::__1::integer_sequence<unsigned long, 0ul>) + 66
31  libcc.dylib                         0x000000015ad0a2fc base::internal::Invoker<base::internal::BindState<void (base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> >::*)(), base::WeakPtr<base::internal::CancelableCallbackImpl<base::RepeatingCallback<void ()> > > >, void ()>::Run(base::internal::BindStateBase*) + 44
32  libaccelerated_widget_mac.dylib     0x0000000178a29d4c base::OnceCallback<void ()>::Run() && + 92
33  libaccelerated_widget_mac.dylib     0x0000000178a281f1 ui::(anonymous namespace)::WrappedTask::Run() + 65
34  libaccelerated_widget_mac.dylib     0x0000000178a2966d void base::internal::FunctorTraits<void (ui::(anonymous namespace)::WrappedTask::*)(), void>::Invoke<void (ui::(anonymous namespace)::WrappedTask::*)(), ui::(anonymous namespace)::WrappedTask*>(void (ui::(anonymous namespace)::WrappedTask::*)(), ui::(anonymous namespace)::WrappedTask*&&) + 125
35  libaccelerated_widget_mac.dylib     0x0000000178a29571 void base::internal::InvokeHelper<false, void>::MakeItSo<void (ui::(anonymous namespace)::WrappedTask::* const&)(), ui::(anonymous namespace)::WrappedTask*>(void (ui::(anonymous namespace)::WrappedTask::* const&&&)(), ui::(anonymous namespace)::WrappedTask*&&) + 81
36  libaccelerated_widget_mac.dylib     0x0000000178a294f5 void base::internal::Invoker<base::internal::BindState<void (ui::(anonymous namespace)::WrappedTask::*)(), base::internal::OwnedWrapper<ui::(anonymous namespace)::WrappedTask> >, void ()>::RunImpl<void (ui::(anonymous namespace)::WrappedTask::* const&)(), std::__1::tuple<base::internal::OwnedWrapper<ui::(anonymous namespace)::WrappedTask> > const&, 0ul>(void (ui::(anonymous namespace)::WrappedTask::* const&&&)(), std::__1::tuple<base::internal::OwnedWrapper<ui::(anonymous namespace)::WrappedTask> > const&&&, std::__1::integer_sequence<unsigned long, 0ul>) + 85
37  libaccelerated_widget_mac.dylib     0x0000000178a293ec base::internal::Invoker<base::internal::BindState<void (ui::(anonymous namespace)::WrappedTask::*)(), base::internal::OwnedWrapper<ui::(anonymous namespace)::WrappedTask> >, void ()>::Run(base::internal::BindStateBase*) + 44
38  libbase.dylib                       0x00000001127f606c base::OnceCallback<void ()>::Run() && + 92
39  libbase.dylib                       0x00000001128359c9 base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) + 729
40  libbase.dylib                       0x00000001128bea4c base::MessageLoopImpl::RunTask(base::PendingTask*) + 796
41  libbase.dylib                       0x00000001128beec9 base::MessageLoopImpl::DeferOrRunPendingTask(base::PendingTask) + 89
42  libbase.dylib                       0x00000001128bf977 base::MessageLoopImpl::DoWork() + 455
43  libbase.dylib                       0x00000001128ca93c base::MessagePumpCFRunLoopBase::RunWork() + 124
44  libbase.dylib                       0x00000001128ca8ac ___ZN4base24MessagePumpCFRunLoopBase13RunWorkSourceEPv_block_invoke + 28
45  libbase.dylib                       0x000000011287f06a base::mac::CallWithEHFrame(void () block_pointer) + 10
46  libbase.dylib                       0x00000001128c9925 base::MessagePumpCFRunLoopBase::RunWorkSource(void*) + 101
47  CoreFoundation                      0x00007fff31788a11 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
48  CoreFoundation                      0x00007fff3184242c __CFRunLoopDoSource0 + 108
49  CoreFoundation                      0x00007fff3176b470 __CFRunLoopDoSources0 + 208
50  CoreFoundation                      0x00007fff3176a8ed __CFRunLoopRun + 1293
51  CoreFoundation                      0x00007fff3176a153 CFRunLoopRunSpecific + 483
52  HIToolbox                           0x00007fff30a54d96 RunCurrentEventLoopInMode + 286
53  HIToolbox                           0x00007fff30a54b06 ReceiveNextEventCommon + 613
54  HIToolbox                           0x00007fff30a54884 _BlockUntilNextEventMatchingListInModeWithFilter + 64
55  AppKit                              0x00007fff2ed05a73 _DPSNextEvent + 2085
56  AppKit                              0x00007fff2f49be34 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 3044
57  libchrome_dll.dylib                 0x000000011b29e87a __71-[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke + 106
58  libbase.dylib                       0x000000011287f06a base::mac::CallWithEHFrame(void () block_pointer) + 10
59  libchrome_dll.dylib                 0x000000011b29e718 -[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 248
60  AppKit                              0x00007fff2ecfa885 -[NSApplication run] + 764
61  libbase.dylib                       0x00000001128cbfb1 base::MessagePumpNSApplication::DoRun(base::MessagePump::Delegate*) + 305
62  libbase.dylib                       0x00000001128c9023 base::MessagePumpCFRunLoopBase::Run(base::MessagePump::Delegate*) + 131
63  libbase.dylib                       0x00000001128be2b0 base::MessageLoopImpl::Run(bool) + 512
64  libbase.dylib                       0x000000011296d5fd base::RunLoop::Run() + 525
65  libchrome_dll.dylib                 0x000000011b2a7746 ChromeBrowserMainParts::MainMessageLoopRun(int*) + 294
66  libcontent.dylib                    0x00000001419dfc9c content::BrowserMainLoop::RunMainMessageLoopParts() + 332
67  libcontent.dylib                    0x00000001419f0088 content::BrowserMainRunnerImpl::Run() + 344
68  libcontent.dylib                    0x00000001419d9a80 content::BrowserMain(content::MainFunctionParams const&) + 208
69  libcontent.dylib                    0x00000001442a0906 content::RunBrowserProcessMain(content::MainFunctionParams const&, content::ContentMainDelegate*) + 134
70  libcontent.dylib                    0x00000001442a1fb4 content::ContentMainRunnerImpl::RunServiceManager(content::MainFunctionParams&, bool) + 1268
71  libcontent.dylib                    0x00000001442a19cb content::ContentMainRunnerImpl::Run(bool) + 603
72  libcontent.dylib                    0x000000014429e399 content::ContentServiceManagerMainDelegate::RunEmbedderProcess() + 57
73  libembedder.dylib                   0x00000001125753d7 service_manager::Main(service_manager::MainParams const&) + 1607
74  libcontent.dylib                    0x00000001442a0839 content::ContentMain(content::ContentMainParams const&) + 89
75  libchrome_dll.dylib                 0x000000011866a82e ChromeMain + 270
76  Chromium                            0x000000010ff1cc53 main + 659
77  libdyld.dylib                       0x00007fff595a7015 start + 1
78  ???                                 0x000000000000001b 0x0 + 27

Ken, could you triage?