In two webkit_layout_tests runs on my CL https://chromium-review.googlesource.com/c/chromium/src/+/920922/8 I see the following crash stacks:

22:21:52.744 6872   [4332:12772:0222/222152.510:FATAL:Document.cpp(2054)] Check failed: (node.IsDocumentNode() || !node.GetLayoutObject() || FlatTreeTraversal::Parent(node)). SUMMARY
22:21:52.744 6872   Backtrace:
22:21:52.744 6872   	base::debug::StackTrace::StackTrace [0x02B22EF0+32]
22:21:52.744 6872   	base::debug::StackTrace::StackTrace [0x02B4C91D+13]
22:21:52.744 6872   	logging::LogMessage::~LogMessage [0x02AC2910+80]
22:21:52.744 6872   	blink::Document::ClearFocusedElementSoon [0x040BB6F8+868]
22:21:52.744 6872   	blink::Document::ClearFocusedElementSoon [0x040BB753+959]
22:21:52.744 6872   	blink::Document::UpdateStyleAndLayoutTree [0x040B83C6+618]
22:21:52.744 6872   	blink::LocalFrameView::UpdateStyleAndLayoutIfNeededRecursiveInternal [0x04262045+137]
22:21:52.744 6872   	blink::LocalFrameView::UpdateStyleAndLayoutIfNeededRecursive [0x04260BE9+95]
22:21:52.744 6872   	blink::LocalFrameView::UpdateLifecyclePhasesInternal [0x0425FFDE+442]
22:21:52.744 6872   	blink::LocalFrameView::UpdateAllLifecyclePhases [0x0425FE22+28]
22:21:52.745 6872   	blink::PageAnimator::UpdateAllLifecyclePhases [0x0461A754+28]
22:21:52.745 6872   	blink::PageWidgetDelegate::UpdateLifecycle [0x04F95778+24]
22:21:52.745 6872   	blink::WebViewImpl::UpdateLifecycle [0x04F0B3E5+133]
22:21:52.745 6872   	blink::WebWidget::UpdateAllLifecyclePhases [0x0492C30A+10]
22:21:52.745 6872   	test_runner::EventSender::MouseMoveTo [0x04ACEF5E+50]
22:21:52.745 6872   	?Run@?$Invoker@U?$BindState@P8WebAXObjectProxy@test_runner@@AE_NABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z$$V@internal@base@@$$A6A_NPAVWebAXObjectProxy@test_runner@@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z [0x04AC3EBF+15]
22:21:52.745 6872   	gin::internal::Dispatcher<void __cdecl(test_runner::EventSenderBindings *,gin::Arguments *)>::DispatchToCallback [0x04AD55B6+198]
22:21:52.745 6872   	v8::internal::FunctionCallbackArguments::Call [0x0205D3F8+456]
22:21:52.745 6872   	v8::internal::Builtins::InvokeApiFunction [0x0211A221+4241]
22:21:52.745 6872   	v8::internal::BuiltinArguments::BuiltinArguments [0x0211903E+494]
22:21:52.745 6872   	v8::internal::Builtin_HandleApiCall [0x02118C71+161]

and

22:16:56.905 29866   [1:1:0222/221656.090180:FATAL:Document.cpp(2054)] Check failed: (node.IsDocumentNode() || !node.GetLayoutObject() || FlatTreeTraversal::Parent(node)). SUMMARY
22:16:56.905 29866   #0 0x0000033d40cc base::debug::StackTrace::StackTrace()
22:16:56.905 29866   #1 0x0000033f2e8c logging::LogMessage::~LogMessage()
22:16:56.905 29866   #2 0x00000515f1f5 blink::AssertLayoutTreeUpdated()
22:16:56.905 29866   #3 0x00000515f215 blink::AssertLayoutTreeUpdated()
22:16:56.905 29866   #4 0x000005159a64 blink::Document::UpdateStyleAndLayoutTree()
22:16:56.905 29866   #5 0x00000541a472 blink::LocalFrameView::UpdateStyleAndLayoutIfNeededRecursiveInternal()
22:16:56.905 29866   #6 0x0000054181e6 blink::LocalFrameView::UpdateStyleAndLayoutIfNeededRecursive()
22:16:56.905 29866   #7 0x00000541694b blink::LocalFrameView::UpdateLifecyclePhasesInternal()
22:16:56.905 29866   #8 0x000005416727 blink::LocalFrameView::UpdateAllLifecyclePhases()
22:16:56.905 29866   #9 0x000005ae257e blink::PageAnimator::UpdateAllLifecyclePhases()
22:16:56.905 29866   #10 0x000005495d78 blink::WebViewImpl::UpdateLifecycle()
22:16:56.905 29866   #11 0x000006d60e4e test_runner::EventSender::MouseMoveTo()
22:16:56.905 29866   #12 0x000006d5e2bb test_runner::EventSenderBindings::MouseMoveTo()
22:16:56.905 29866   #13 0x000006d6b35a gin::internal::Dispatcher<>::DispatchToCallback()
22:16:56.905 29866   #14 0x000001f43e7e v8::internal::FunctionCallbackArguments::Call()
22:16:56.905 29866   #15 0x000002022920 v8::internal::(anonymous namespace)::HandleApiCallHelper<>()
22:16:56.905 29866   #16 0x000002020de9 v8::internal::Builtin_Impl_HandleApiCall()
22:16:56.905 29866   #17 0x00000202082d v8::internal::Builtin_HandleApiCall()
22:16:56.905 29866   #18 0x356d44904264 <unknown>

It looks like this assertion was introduced in https://chromium-review.googlesource.com/c/chromium/src/+/920329.