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chromium/third_party/blink/web_tests/external/wpt/editing/crashtests/designMode-document-will-be-blurred-by-focus-event-listener.html 

<!DOCTYPE html>
<html class="test-wait">
<meta charset="utf-8">
<script>
addEventListener("load", () => {
  const parentDocument = document;
  const iframe = parentDocument.querySelector("iframe");
  iframe.contentDocument.designMode = "on";
  iframe.contentWindow.addEventListener("focus", () => {
    iframe.contentDocument.execCommand("insertText", false, "def");
    iframe.parentElement.setAttribute("hidden", "hidden");
    setTimeout(() => parentDocument.documentElement.removeAttribute("class"), 0);
  });
  iframe.contentWindow.focus();
});
</script>
<div><iframe srcdoc="<div>abc</div>"></iframe></div>
</html>