Our web-platform-tests imports are currently blocked because the CQ bots are hitting a DCHECK when running the following new tests:
* virtual/incremental-shadow-dom/external/wpt/css/css-scoping/shadow-fallback-dynamic-002.html
* virtual/incremental-shadow-dom/external/wpt/css/css-scoping/shadow-fallback-dynamic-003.html
* virtual/incremental-shadow-dom/external/wpt/css/css-scoping/shadow-fallback-dynamic-005.html

The backtrace looks like this:
crash log for renderer (pid <unknown>):
STDOUT: #CRASHED - renderer
STDERR: 
STDERR: DevTools listening on ws://127.0.0.1:43884/devtools/browser/a7a3b13c-b565-4335-a8fb-d2641b28733b
STDERR: [1:1:0316/021352.946589:FATAL:Document.cpp(2068)] Check failed: (node.IsDocumentNode() || !node.GetLayoutObject() || FlatTreeTraversal::Parent(node)). #text "FAIL"
STDERR: #0 0x0000034150ec base::debug::StackTrace::StackTrace()
STDERR: #1 0x000003433e4c logging::LogMessage::~LogMessage()
STDERR: #2 0x00000516acf5 blink::AssertLayoutTreeUpdated()
STDERR: #3 0x00000516ad15 blink::AssertLayoutTreeUpdated()
STDERR: #4 0x000005165544 blink::Document::UpdateStyleAndLayoutTree()
STDERR: #5 0x00000517b2ea blink::Document::FinishedParsing()
STDERR: #6 0x000005570d1a blink::HTMLConstructionSite::FinishedParsing()
STDERR: #7 0x0000055ce7b4 blink::HTMLTreeBuilder::Finished()
STDERR: #8 0x00000555dde6 blink::HTMLDocumentParser::end()
STDERR: #9 0x000005557db8 blink::HTMLDocumentParser::AttemptToRunDeferredScriptsAndEnd()
STDERR: #10 0x000005557c74 blink::HTMLDocumentParser::PrepareToStopParsing()
STDERR: #11 0x00000555aeb7 blink::HTMLDocumentParser::ProcessTokenizedChunkFromBackgroundParser()
STDERR: #12 0x00000555898a blink::HTMLDocumentParser::PumpPendingSpeculations()
STDERR: #13 0x0000055584c9 blink::HTMLDocumentParser::ResumeParsingAfterYield()
STDERR: #14 0x000002a71100 WTF::ThreadCheckingCallbackWrapper<>::Run()
STDERR: #15 0x000004cb26da blink::TaskHandle::Runner::Run()
STDERR: #16 0x000001adebcd _ZN4base8internal7InvokerINS0_9BindStateIMN5media12PipelineImplEFvRKN3gfx4SizeEEJNS_7WeakPtrIS4_EES6_EEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #17 0x000002a71100 WTF::ThreadCheckingCallbackWrapper<>::Run()
STDERR: #18 0x0000034166ff base::debug::TaskAnnotator::RunTask()
STDERR: #19 0x000002acb206 blink::scheduler::internal::ThreadControllerImpl::DoWork()
STDERR: #20 0x000001a6e1d8 _ZN4base8internal7InvokerINS0_9BindStateIMN7network17ResourceScheduler28ScheduledResourceRequestImplEFvNS3_12_GLOBAL__N_19StartModeEEJNS_7WeakPtrIS5_EES7_EEEFvvEE7RunOnceEPNS0_13BindStateBaseE
STDERR: #21 0x0000034166ff base::debug::TaskAnnotator::RunTask()
STDERR: #22 0x00000343b4f6 base::internal::IncomingTaskQueue::RunTask()
STDERR: #23 0x000003439977 base::MessageLoop::RunTask()
STDERR: #24 0x000003439d9a base::MessageLoop::DeferOrRunPendingTask()
STDERR: #25 0x00000343a02e base::MessageLoop::DoWork()
STDERR: #26 0x00000343db59 base::MessagePumpDefault::Run()
STDERR: #27 0x0000034391ec base::MessageLoop::Run()
STDERR: #28 0x000003462256 base::RunLoop::Run()
STDERR: #29 0x000006843fbb content::RendererMain()
STDERR: #30 0x000002b33224 content::RunZygote()
STDERR: #31 0x000002b33a04 content::RunNamedProcessTypeMain()
STDERR: #32 0x000002b34b03 content::ContentMainRunnerImpl::Run()
STDERR: #33 0x0000049fb83a service_manager::Main()
STDERR: #34 0x000001ee6fc4 content::ContentMain()
STDERR: #35 0x000001453139 main
STDERR: #36 0x7f71b7d0ef45 __libc_start_main
STDERR: #37 0x00000145302a _start

These tests came from Mozilla, and were added in commit https://github.com/w3c/web-platform-tests/commit/2eef29f3c0fb7c5f93ece18138c7c780840f4823

For now, I am going to mark them as crashing to unblock our imports.