[Document-customElementRegistry.html]
  [customElementRegistry on a document should return window.customElements by default]
    expected: FAIL

  [customElementRegistry on a document without a browsing context should return null]
    expected: FAIL

  [customElementRegistry on a document of a connected iframe should return contentWindow.customElements]
    expected: FAIL

  [customElementRegistry on a document of a disconnected iframe should return contentWindow.customElements]
    expected: FAIL
