<style>
  iframe, iframe::-webkit-scrollbar {
    block-size: 0;
  }
</style>
<script>
  onload = () => {
    if (window.testRunner) {
      testRunner.dumpAsText();
      testRunner.waitUntilDone();
    }
    document.designMode = 'on';
    let iframe0 = document.createElement('iframe');
    document.body.appendChild(iframe0);
    document.body.appendChild(document.createElement('iframe'));
    getSelection().collapse(document.body, 0);
    getSelection().extend(document.body);
    iframe0.contentDocument.onvisibilitychange = () => {
      document.execCommand('InsertHTML', false, 'foo');
    };
    setTimeout(function() { document.write("PASS. WebKit didn't crash."); testRunner.notifyDone(); }, 1000);
  };
</script>