Issue found by rbpotter@.

Minimal repro example attached (also pasting below). Need to have DCHECKs enabled to reproduce. Note that this is blocking WebUIs migration to Polymer 2 (which uses Shadow DOM v1)

<button>Click to show dialog</button>
<custom-dialog>
  <list-item></list-item>
</custom-dialog>

<script>
  customElements.define('list-item', class extends HTMLElement {
    constructor() {
      super();
      const shadowRoot = this.attachShadow({mode: 'open'});
      shadowRoot.innerHTML = '<div></div>';
    }
  });

  customElements.define('custom-dialog', class extends HTMLElement {
    constructor() {
      super();
      const shadowRoot = this.attachShadow({mode: 'open'});
      shadowRoot.innerHTML = '<dialog><slot></slot></dialog>';
    }

    show() {
      this.shadowRoot.querySelector('dialog').showModal();
    }
  });

  const b = document.body.querySelector('button');
  b.addEventListener('click', () => {
    const el = document.body.querySelector('custom-dialog');
    el.show();
  });
</script>


Pasting stacktrace below.

1:1:0607/123312.503686:FATAL:document.cc(2071)] Check failed: !node.NeedsReattachLayoutTree(). 
#0 0x7f2e6b931f6c base::debug::StackTrace::StackTrace()
#1 0x7f2e6b87b6db logging::LogMessage::~LogMessage()
#2 0x7f2e63346a39 blink::AssertLayoutTreeUpdated()
#3 0x7f2e633469b2 blink::AssertLayoutTreeUpdated()
#4 0x7f2e63341124 blink::Document::UpdateStyleAndLayoutTree()
#5 0x7f2e63347990 blink::Document::UpdateStyleAndLayoutTreeIgnorePendingStylesheets()
#6 0x7f2e63347172 blink::Document::UpdateStyleAndLayoutIgnorePendingStylesheets()
#7 0x7f2e637eed64 blink::HTMLDialogElement::showModal()
#8 0x7f2e640623dd blink::V8HTMLDialogElement::showModalMethodCallback()
#9 0x7f2e648d4813 v8::internal::FunctionCallbackArguments::Call()
#10 0x7f2e648d2b72 v8::internal::(anonymous namespace)::HandleApiCallHelper<>()
#11 0x7f2e648d0f38 v8::internal::Builtin_Impl_HandleApiCall()
#12 0x7f2e648d097d v8::internal::Builtin_HandleApiCall()
#13 0x7f2e654deed5 <unknown>

 

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