Browser Plugin: Simplified guest attachment

content/test/data/browser_plugin_embedder.html

 <script type="text/javascript">
 function SetSrc(src) {
   var plugin = document.getElementById('plugin');
   plugin.src = src;
 }
 function SetSize(w, h) {
   var plugin = document.getElementById('plugin');
   plugin.width = w;
   plugin.height = h;
 }
@@ skipping 35 matching lines @@
       window.document.title = name;
     } else {
       window.document.title = 'main guest';
     }
   }
 }
 
 var plugin = document.getElementById('plugin');
 window.addEventListener('message', receiveMessage, false);
 plugin.addEventListener('-internal-instanceid-allocated', function(e) {
-  plugin['-internal-attach']({});
+  var detail = e.detail ? JSON.parse(e.detail) : {};
+  plugin['-internal-attach'](detail.windowId, {});
 });
 </script>