On a try job for https://chromium-review.googlesource.com/c/770492/ at r517032, which has nothing to do with Viz, I got a test failure.

https://build.chromium.org/p/tryserver.chromium.chromiumos/builders/linux-chromeos-rel/builds/4331

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[23233:23233:1116/020052.578421:ERROR:gles2_cmd_decoder.cc(5472)] Error: 5 for Command kLoseContextCHROMIUM
[23233:23233:1116/020052.578498:ERROR:gpu_channel_manager.cc(200)] Exiting GPU process because some drivers cannot recover from problems.
[23233:23233:1116/020052.578818:FATAL:frame_sink_manager_impl.cc(51)] Check failed: (thread_checker_).CalledOnValidThread(). 
#0 0x0000028fd9bc base::debug::StackTrace::StackTrace()
#1 0x0000029105dc logging::LogMessage::~LogMessage()
#2 0x000003bb1a2b viz::FrameSinkManagerImpl::~FrameSinkManagerImpl()
#3 0x000003bb1e0e viz::FrameSinkManagerImpl::~FrameSinkManagerImpl()
#4 0x00000244dfda viz::VizMainImpl::~VizMainImpl()
#5 0x00000518e065 content::GpuChildThread::~GpuChildThread()
#6 0x00000518e125 content::GpuChildThread::~GpuChildThread()
#7 0x000003ce5d44 content::ChildProcess::~ChildProcess()
#8 0x00000518c53d content::GpuMain()
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[23211:23211:1116/020052.869507:FATAL:begin_frame_source.cc(329)] Check failed: (args.source_id != last_args.source_id) || (args.sequence_number > last_args.sequence_number). current {"type":"BeginFrameArgs","subtype":"MISSED","source_id":2,"sequence_number":1,"frame_time_us":349252696.0,"deadline_us":349269362.0,"interval_us":16666.0,"on_critical_path":true}, last {"type":"BeginFrameArgs","subtype":"MISSED","source_id":2,"sequence_number":10,"frame_time_us":348919376.0,"deadline_us":348936042.0,"interval_us":16666.0,"on_critical_path":true}
#0 0x0000028fd9bc base::debug::StackTrace::StackTrace()
#1 0x0000029105dc logging::LogMessage::~LogMessage()
#2 0x00000382a7bc viz::ExternalBeginFrameSource::OnBeginFrame()
#3 0x000003c5fbc6 viz::ClientLayerTreeFrameSink::OnBeginFrame()
#4 0x000001045811 viz::mojom::CompositorFrameSinkClientStubDispatch::Accept()
#5 0x0000025e381b mojo::InterfaceEndpointClient::HandleValidatedMessage()
#6 0x0000025e3406 mojo::FilterChain::Accept()
...
#24 0x00000293aa68 base::RunLoop::Run()
#25 0x000002532c56 content::MessageLoopRunner::Run()
#26 0x000002518263 content::DOMMessageQueue::WaitForMessage()
#27 0x000002517630 content::(anonymous namespace)::ExecuteScriptHelper()
#28 0x000002517072 content::ExecuteScriptAndExtractString()
#29 0x000000953fbe content::WebRtcContentBrowserTestBase::ExecuteJavascriptAndReturnResult()
#30 0x0000009542c0 content::WebRtcContentBrowserTestBase::ExecuteJavascriptAndWaitForOk()
#31 0x000000954180 content::WebRtcContentBrowserTestBase::MakeTypicalCall()
#32 0x000000950b70 content::WebRtcCaptureFromElementBrowserTest_CaptureFromOpaqueCanvas2DHandlesContextLoss_Test::RunTestOnMainThread()

...
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