chromium/third_party/blink/web_tests/http/tests/serviceworker/resources/windowclient-focus.html

<!DOCTYPE html>
<html>
<head>
  <title>Resource for WindowClient.focus() tests</title>
</head>
<body>
  <div>This is resources/window-client-focus.html</div>
</body>
<script>
  function insertFrame(name) {
    var frame = document.createElement('iframe');
    frame.src = 'windowclient-focus.html?' + name;
    document.body.appendChild(frame);
  }

  if (location.search == "") {
    // If this window is the top level window, we should insert two iframes.
    // They shouldn't create new iframes.
    insertFrame("1");
    insertFrame("2");
  }
</script>
</html>