As of d1d8274829c9686c2f6, launching, closing (by pressing the frame X button), and relaunching the KSV  app causes a crash when using chrome --enable-features=KeyboardShortcutViewerApp

The stack:

[61937:61937:0620/131109.406447:FATAL:host_frame_sink_manager.cc(69)] Check failed: !data.IsFrameSinkRegistered(). 
#0 0x7f1ca3d2030c base::debug::StackTrace::StackTrace()
#1 0x7f1ca3c7002b logging::LogMessage::~LogMessage()
#2 0x7f1c9e44f54b viz::HostFrameSinkManager::RegisterFrameSinkId()
#3 0x7f1c9499690f ui::ws2::ClientRoot::RegisterVizEmbeddingSupport()
#4 0x7f1c949a98dd ui::ws2::WindowTree::NewTopLevelWindow()
#5 0x7f1c949bfd9d ui::mojom::WindowTreeStubDispatch::Accept()
#6 0x7f1ca2fd2996 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#7 0x7f1ca2fd22c6 mojo::FilterChain::Accept()
#8 0x7f1ca2fd3d25 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#9 0x7f1ca2fda49c mojo::internal::MultiplexRouter::ProcessIncomingMessage()
#10 0x7f1ca2fd98a0 mojo::internal::MultiplexRouter::Accept()
#11 0x7f1ca2fd22c6 mojo::FilterChain::Accept()
#12 0x7f1ca2fcd503 mojo::Connector::ReadSingleMessage()
#13 0x7f1ca2fcdf51 mojo::Connector::ReadAllAvailableMessages()
#14 0x7f1ca2fcddf9 mojo::Connector::OnHandleReadyInternal()
#15 0x7f1ca2fce647 mojo::SimpleWatcher::DiscardReadyState()
#16 0x7f1ca2fad594 mojo::SimpleWatcher::OnHandleReady()
#17 0x7f1ca2fadaa1 _ZN4base8internal7InvokerINS0_9BindStateIMN4mojo13SimpleWatcherEFvijRKNS3_18HandleSignalsStateEEJNS_7WeakPtrIS4_EEijS5_EEEFvvEE7RunImplIRKS9_RKNSt3__15tupleIJSB_ijS5_EEEJLm0ELm1ELm2ELm3EEEEvOT_OT0_NSI_16integer_sequenceImJXspT1_EEEE
#18 0x7f1ca3c53025 base::debug::TaskAnnotator::RunTask()
#19 0x7f1ca3c7c879 base::internal::IncomingTaskQueue::RunTask()
#20 0x7f1ca3c8004b base::MessageLoop::RunTask()
#21 0x7f1ca3c803da base::MessageLoop::DeferOrRunPendingTask()
#22 0x7f1ca3c8063c base::MessageLoop::DoWork()
#23 0x7f1ca3d40389 base::MessagePumpLibevent::Run()
#24 0x7f1ca3c7fa34 base::MessageLoop::Run()
#25 0x7f1ca3cb2399 base::RunLoop::Run()
#26 0x556aae647c6b ChromeBrowserMainParts::MainMessageLoopRun()
#27 0x7f1ca0ed7ae7 content::BrowserMainLoop::RunMainMessageLoopParts()
#28 0x7f1ca0eda866 content::BrowserMainRunnerImpl::Run()
#29 0x7f1ca0ed3d64 content::BrowserMain()
#30 0x7f1ca1909b53 content::RunBrowserProcessMain()
#31 0x7f1ca190ab18 content::ContentMainRunnerImpl::Run()
#32 0x7f1ca3fd38cc service_manager::Main()
#33 0x7f1ca1908b74 content::ContentMain()
#34 0x556aadadbcd3 ChromeMain
#35 0x7f1c959bf2b1 __libc_start_main
#36 0x556aadadbb4a _start

Received signal 6
#0 0x7f1ca3d2030c base::debug::StackTrace::StackTrace()
#1 0x7f1ca3d1fe01 base::debug::(anonymous namespace)::StackDumpSignalHandler()
#2 0x7f1c970840c0 <unknown>
#3 0x7f1c959d1fcf gsignal
#4 0x7f1c959d33fa abort
#5 0x7f1ca3d1ec95 base::debug::BreakDebugger()
#6 0x7f1ca3c703e8 logging::LogMessage::~LogMessage()
#7 0x7f1c9e44f54b viz::HostFrameSinkManager::RegisterFrameSinkId()
#8 0x7f1c9499690f ui::ws2::ClientRoot::RegisterVizEmbeddingSupport()
#9 0x7f1c949a98dd ui::ws2::WindowTree::NewTopLevelWindow()
#10 0x7f1c949bfd9d ui::mojom::WindowTreeStubDispatch::Accept()
#11 0x7f1ca2fd2996 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#12 0x7f1ca2fd22c6 mojo::FilterChain::Accept()
#13 0x7f1ca2fd3d25 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#14 0x7f1ca2fda49c mojo::internal::MultiplexRouter::ProcessIncomingMessage()
#15 0x7f1ca2fd98a0 mojo::internal::MultiplexRouter::Accept()
#16 0x7f1ca2fd22c6 mojo::FilterChain::Accept()
#17 0x7f1ca2fcd503 mojo::Connector::ReadSingleMessage()
#18 0x7f1ca2fcdf51 mojo::Connector::ReadAllAvailableMessages()
#19 0x7f1ca2fcddf9 mojo::Connector::OnHandleReadyInternal()
#20 0x7f1ca2fce647 mojo::SimpleWatcher::DiscardReadyState()
#21 0x7f1ca2fad594 mojo::SimpleWatcher::OnHandleReady()
#22 0x7f1ca2fadaa1 _ZN4base8internal7InvokerINS0_9BindStateIMN4mojo13SimpleWatcherEFvijRKNS3_18HandleSignalsStateEEJNS_7WeakPtrIS4_EEijS5_EEEFvvEE7RunImplIRKS9_RKNSt3__15tupleIJSB_ijS5_EEEJLm0ELm1ELm2ELm3EEEEvOT_OT0_NSI_16integer_sequenceImJXspT1_EEEE
#23 0x7f1ca3c53025 base::debug::TaskAnnotator::RunTask()
#24 0x7f1ca3c7c879 base::internal::IncomingTaskQueue::RunTask()
#25 0x7f1ca3c8004b base::MessageLoop::RunTask()
#26 0x7f1ca3c803da base::MessageLoop::DeferOrRunPendingTask()
#27 0x7f1ca3c8063c base::MessageLoop::DoWork()
#28 0x7f1ca3d40389 base::MessagePumpLibevent::Run()
#29 0x7f1ca3c7fa34 base::MessageLoop::Run()
#30 0x7f1ca3cb2399 base::RunLoop::Run()
#31 0x556aae647c6b ChromeBrowserMainParts::MainMessageLoopRun()
#32 0x7f1ca0ed7ae7 content::BrowserMainLoop::RunMainMessageLoopParts()
#33 0x7f1ca0eda866 content::BrowserMainRunnerImpl::Run()
#34 0x7f1ca0ed3d64 content::BrowserMain()
#35 0x7f1ca1909b53 content::RunBrowserProcessMain()
#36 0x7f1ca190ab18 content::ContentMainRunnerImpl::Run()
#37 0x7f1ca3fd38cc service_manager::Main()
#38 0x7f1ca1908b74 content::ContentMain()
#39 0x556aadadbcd3 ChromeMain
#40 0x7f1c959bf2b1 __libc_start_main
#41 0x556aadadbb4a _start