<body>
    Child.
    <iframe id="grandchild" src="change_grandchild.html"></iframe>
</body>
<script>
    var timer = window.setInterval(poll, 100);
    function poll() {
        if (document.body.getAttribute("data-contains-grandchild")) {
            var grandchild = document.getElementById("grandchild");
            window.frameElement.parentNode.appendChild(grandchild);
            window.clearTimeout(timer);
        }
    }
</script>
