A bunch of tab capture tests have started failing on Mac while running in Viz.

First failing build: https://ci.chromium.org/buildbot/chromium.fyi/mac-views-rel/1947

I can reproduce on ToT today locally. From the failure it looks like 0 size requests are being sent to Viz. Here's an example failure:

[ RUN      ] SnapshotBrowserTest.AsyncMultiWindowTest

DevTools listening on ws://127.0.0.1:54574/devtools/browser/d1222580-b45a-49f2-ab7c-fe53e646f4a0
[19278:775:0604/120118.623403:ERROR:delegated_frame_host.cc(179)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[19278:775:0604/120118.909542:ERROR:delegated_frame_host.cc(179)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[19278:775:0604/120118.935338:ERROR:delegated_frame_host.cc(179)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[19278:775:0604/120118.960401:ERROR:delegated_frame_host.cc(179)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[19279:23555:0604/120118.911680:FATAL:root_compositor_frame_sink_impl.cc(74)] Check failed: !size.IsEmpty(). 
0   Content Shell Framework             0x000000010e00d01c base::debug::StackTrace::StackTrace(unsigned long) + 28
1   Content Shell Framework             0x000000010df36f6f logging::LogMessage::~LogMessage() + 223
2   Content Shell Framework             0x000000010f90e901 non-virtual thunk to viz::RootCompositorFrameSinkImpl::Resize(gfx::Size const&) + 97
3   Content Shell Framework             0x000000010bf375e3 viz::mojom::DisplayPrivateStubDispatch::Accept(viz::mojom::DisplayPrivate*, mojo::Message*) + 1747
4   Content Shell Framework             0x000000010e1328b6 mojo::InterfaceEndpointClient::HandleValidatedMessage(mojo::Message*) + 982
5   Content Shell Framework             0x000000010e132166 mojo::FilterChain::Accept(mojo::Message*) + 150
6   Content Shell Framework             0x000000010e133c95 mojo::InterfaceEndpointClient::HandleIncomingMessage(mojo::Message*) + 117
7   Content Shell Framework             0x000000010e13a32c mojo::internal::MultiplexRouter::ProcessIncomingMessage(mojo::internal::MultiplexRouter::MessageWrapper*, mojo::internal::MultiplexRouter::ClientCallBehavior, base::SequencedTaskRunner*) + 1420
8   Content Shell Framework             0x000000010e139730 mojo::internal::MultiplexRouter::Accept(mojo::Message*) + 368
9   Content Shell Framework             0x000000010e132166 mojo::FilterChain::Accept(mojo::Message*) + 150
10  Content Shell Framework             0x000000010e12d4a3 mojo::Connector::ReadSingleMessage(unsigned int*) + 419
11  Content Shell Framework             0x000000010e12df01 mojo::Connector::ReadAllAvailableMessages() + 97
12  Content Shell Framework             0x000000010e12ddb9 mojo::Connector::OnHandleReadyInternal(unsigned int) + 137
13  Content Shell Framework             0x000000010bf78c67 mojo::SimpleWatcher::DiscardReadyState(base::RepeatingCallback<void (unsigned int)> const&, unsigned int, mojo::HandleSignalsState const&) + 103
14  Content Shell Framework             0x000000010e03643d mojo::SimpleWatcher::OnHandleReady(int, unsigned int, mojo::HandleSignalsState const&) + 365
15  Content Shell Framework             0x000000010e036961 void base::internal::Invoker<base::internal::BindState<void (mojo::SimpleWatcher::*)(int, unsigned int, mojo::HandleSignalsState const&), base::WeakPtr<mojo::SimpleWatcher>, int, unsigned int, mojo::HandleSignalsState>, void ()>::RunImpl<void (mojo::SimpleWatcher::* const&)(int, unsigned int, mojo::HandleSignalsState const&), std::__1::tuple<base::WeakPtr<mojo::SimpleWatcher>, int, unsigned int, mojo::HandleSignalsState> const&, 0ul, 1ul, 2ul, 3ul>(void (mojo::SimpleWatcher::* const&&&)(int, unsigned int, mojo::HandleSignalsState const&), std::__1::tuple<base::WeakPtr<mojo::SimpleWatcher>, int, unsigned int, mojo::HandleSignalsState> const&&&, std::__1::integer_sequence<unsigned long, 0ul, 1ul, 2ul, 3ul>) + 193
16  Content Shell Framework             0x000000010df1cbe3 base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) + 323
17  Content Shell Framework             0x000000010df4ed29 base::internal::IncomingTaskQueue::RunTask(base::PendingTask*) + 121
18  Content Shell Framework             0x000000010df52bd7 base::MessageLoop::RunTask(base::PendingTask*) + 599
19  Content Shell Framework             0x000000010df52f9a base::MessageLoop::DeferOrRunPendingTask(base::PendingTask) + 186
20  Content Shell Framework             0x000000010df5320c base::MessageLoop::DoWork() + 572
21  Content Shell Framework             0x000000010df55d68 base::MessagePumpDefault::Run(base::MessagePump::Delegate*) + 216
22  Content Shell Framework             0x000000010df525b4 base::MessageLoop::Run(bool) + 132
23  Content Shell Framework             0x000000010df871d9 base::RunLoop::Run() + 249
24  Content Shell Framework             0x000000010dfd453e base::Thread::Run(base::RunLoop*) + 206
25  Content Shell Framework             0x000000010dfd4a7e base::Thread::ThreadMain() + 782
26  Content Shell Framework             0x000000010e01c1ff base::(anonymous namespace)::ThreadFunc(void*) + 95
27  libsystem_pthread.dylib             0x00007fff7f7a26c1 _pthread_body + 340
28  libsystem_pthread.dylib             0x00007fff7f7a256d _pthread_body + 0
29  libsystem_pthread.dylib             0x00007fff7f7a1c5d thread_start + 13


samans@ any insight? Nothing in the changelist of the failure run instantly stood out to me.