content/test/data/browser_plugin_post_message_guest.html

<script>
  var embedder;
  function receiveMessage(event) {
    embedder = event.source;
    if (event.data !== 'stop') {
      event.source.postMessage('foobar', '*');
    } else {
      if (event.data !== '') {
        event.source.postMessage('stop_ack ' + window.name, '*');
      }
    }
  }
  window.addEventListener('message', receiveMessage, false);
  function CreateChildFrame(src) {
    var ifrm = document.createElement("IFRAME");
    ifrm.style.width = "640px";
    ifrm.style.height = "480px";
    ifrm.src = src;
    ifrm.name = 'iframe';
    document.body.appendChild(ifrm);
    embedder.postMessage('ready', '*');
  }
</script>