Repro on Linux with target_os="chromeos" and a debug build:

 ninja -C out/Default -j 1000 -l 20 views_mus_unittests && out/Default/views_mus_unittests --gtest_filter="NativeWidgetMus*"

The tests will all pass, but in the logs you'll see a process crashing due to NOTREACHED. It must not be the test process -- maybe the window server?

[32304:32304:0409/103042:90502674548:FATAL:compositor.cc(441)] Check failed: false. 
#0 0x7f3e189b08fe base::debug::StackTrace::StackTrace()
#1 0x7f3e18a064fc logging::LogMessage::~LogMessage()
#2 0x7f3e15a866eb ui::Compositor::DidFailToInitializeOutputSurface()
#3 0x7f3e1864db90 cc::LayerTreeHost::DidFailToInitializeOutputSurface()
#4 0x7f3e18710205 cc::SingleThreadProxy::SetOutputSurface()
#5 0x7f3e1864d3ba cc::LayerTreeHost::SetOutputSurface()
#6 0x7f3e15a8563d ui::Compositor::SetOutputSurface()
#7 0x7f3e18d8f3ce views::SurfaceContextFactory::CreateOutputSurface()
#8 0x7f3e15a86659 ui::Compositor::RequestNewOutputSurface()
#9 0x7f3e1864d82d cc::LayerTreeHost::RequestNewOutputSurface()
#10 0x7f3e1870fcfd cc::SingleThreadProxy::RequestNewOutputSurface()
#11 0x7f3e18412bf9 _ZN4base8internal15RunnableAdapterIMN2cc18FrameTimingTrackerEFvvEE3RunIJEEEvPS3_DpOT_
#12 0x7f3e18438fe0 _ZN4base8internal12InvokeHelperILb1EvNS0_15RunnableAdapterIMN2cc28ScrollbarAnimationControllerEFvvEEEE8MakeItSoINS_7WeakPtrIS4_EEJEEEvS7_T_DpOT0_
#13 0x7f3e18716ead _ZN4base8internal7InvokerINS_13IndexSequenceIJLm0EEEENS0_9BindStateINS0_15RunnableAdapterIMN2cc17SingleThreadProxyEFvvEEEFvPS7_EJNS_7WeakPtrIS7_EEEEENS0_12InvokeHelperILb1EvSA_EEFvvEE3RunEPNS0_13BindStateBaseE
#14 0x7f3e1843905e base::Callback<>::Run()
#15 0x7f3e18438d69 base::CancelableCallback<>::Forward()
#16 0x7f3e18412bf9 _ZN4base8internal15RunnableAdapterIMN2cc18FrameTimingTrackerEFvvEE3RunIJEEEvPS3_DpOT_
#17 0x7f3e18438fe0 _ZN4base8internal12InvokeHelperILb1EvNS0_15RunnableAdapterIMN2cc28ScrollbarAnimationControllerEFvvEEEE8MakeItSoINS_7WeakPtrIS4_EEJEEEvS7_T_DpOT0_
#18 0x7f3e18438f8d _ZN4base8internal7InvokerINS_13IndexSequenceIJLm0EEEENS0_9BindStateINS0_15RunnableAdapterIMNS_18CancelableCallbackIFvvEEEKFvvEEEFvPKS8_EJNS_7WeakPtrIS8_EEEEENS0_12InvokeHelperILb1EvSB_EES7_E3RunEPNS0_13BindStateBaseE
#19 0x7f3e1899486e base::Callback<>::Run()
#20 0x7f3e189b60ae base::debug::TaskAnnotator::RunTask()
#21 0x7f3e18a21c81 base::MessageLoop::RunTask()
#22 0x7f3e18a21f08 base::MessageLoop::DeferOrRunPendingTask()
#23 0x7f3e18a220d2 base::MessageLoop::DoWork()
#24 0x7f3e18a31ef4 base::MessagePumpDefault::Run()
#25 0x7f3e18a216fa base::MessageLoop::RunHandler()
#26 0x7f3e18ab33f4 base::RunLoop::Run()
#27 0x7f3e0b38ba72 mojo::ApplicationRunner::Run()
#28 0x7f3e0b38bb3c mojo::ApplicationRunner::Run()
#29 0x7f3e0b245d82 MojoMain
#30 0x00000076072f mojo::shell::RunNativeApplication()
#31 0x0000005cb36e mojo::shell::(anonymous namespace)::RunNativeLibrary()
#32 0x0000005cc5a5 _ZN4base8internal15RunnableAdapterIPFvPvN4mojo16InterfaceRequestINS3_5shell5mojom11ShellClientEEEEE3RunIJRKS2_S8_EEEvDpOT_
#33 0x0000005cc52a _ZN4base8internal12InvokeHelperILb0EvNS0_15RunnableAdapterIPFvPvN4mojo16InterfaceRequestINS4_5shell5mojom11ShellClientEEEEEEE8MakeItSoIJRKS3_S9_EEEvSC_DpOT_
#34 0x0000005cc4e9 _ZN4base8internal7InvokerINS_13IndexSequenceIJLm0EEEENS0_9BindStateINS0_15RunnableAdapterIPFvPvN4mojo16InterfaceRequestINS7_5shell5mojom11ShellClientEEEEEESD_JRS6_EEENS0_12InvokeHelperILb0EvSF_EEFvSC_EE3RunEPNS0_13BindStateBaseEOSC_
#35 0x0000005afd73 base::Callback<>::Run()
#36 0x00000075ff48 mojo::shell::ChildProcessMain()
#37 0x0000005cb198 mojo::shell::ChildProcessMain()
#38 0x0000005b0ec6 mojo::shell::(anonymous namespace)::RunChildProcess()
#39 0x0000005b0e7b main
#40 0x7f3e11d19ec5 __libc_start_main
#41 0x0000004a17e9 <unknown>