update-widget-positions-on-nested-frames-and-scrollers-outer-frame.html

<!DOCTYPE html>
<html>
<head>
  <style>
    iframe {
      height: 900px;
    }

    div {
      height: 300px;
      overflow: auto;
      border: 1px solid black;
    }
  </style>
  <script>
    // We expect to get a message from the inner frame to tell us when
    // the inner frame's DOM is all set up. We need to scroll down from
    // this frame, and then, unfortunately, transfer control back to the
    // inner frame so that it can click on one of the select elements.
    window.onmessage = function() {
      document.getElementById('scrollable').scrollTop = 500;
      document.getElementById('frame').contentWindow.postMessage('', '*');
    };
  </script>
</head>

<body>
  <div id='scrollable'>
    <iframe id='frame' src='update-widget-positions-on-nested-frames-and-scrollers-inner-frame.html'></iframe>
  </div>
</body>
</html>

chromium/third_party/blink/web_tests/compositing/overflow/resources/update-widget-positions-on-nested-frames-and-scrollers-outer-frame.html