<body>
  <a id="link" href="joint-session-history-child2.html">Child1</a>.
  <iframe id="grandchild"></iframe>
</body>
<script>
  window.onload = function() {
    var link = document.getElementById("link");
    var grandchild = document.getElementById("grandchild");
    var timer = window.setInterval(poll, 100);
    function poll() {
      if (grandchild.getAttribute("data-grandchild-loaded")) {
        window.clearInterval(timer);
        link.click();
      }
    }
    grandchild.src="joint-session-history-grandchild1.html";
  };
</script>
