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chromium/content/test/data/render_frame_host/focus.html 

<!DOCTYPE html>
<html>
<head>
</head>
<body>
  <iframe name='frame1' src='data:text/html,<input><div>frame1</div>'></iframe>
  <iframe name='frame2' src='data:text/html,<input><div>frame2</div>'></iframe>
  <iframe name='frame3' src='data:text/html,<iframe%20name=%27frame4%27%20src=%27data:text/html,<input><div>frame4</div>%27></iframe>'></iframe>
</body>
<script>
  function focusframe1() {
    frames[0].focus();
  }
  function focusframe2() {
    frames[1].focus();
  }
  function focusframe4() {
    frames[2][0].focus();
  }
  function detachframe(i) {
    var iframes = document.getElementsByTagName('iframe');
    iframes[i - 1].parentNode.removeChild(iframes[i - 1]);
  }
</script>
</html>