chromium/third_party/blink/web_tests/fast/dom/nodesFromRect/resources/child-frame-scrolled.html

<!DOCTYPE html>
<html>
<head>
<style type="text/css">
    body { margin: 0px; }
    #content {
        width: 200px;
        height: 1000px;
    }
</style>
</head>
<body>
    <div id="content"></div>
</body>

<script>
  document.scrollingElement.scrollTop = "400";
  top.debug("iframe's scroll top is " + document.scrollingElement.scrollTop);
  top.postMessage("subframe-loaded", "*");
</script>
</html>