Browser Plugin: Add HTML5-like postMessage support

content/test/data/browser_plugin_post_message_guest.html

Index: content/test/data/browser_plugin_post_message_guest.html
diff --git a/content/test/data/browser_plugin_post_message_guest.html b/content/test/data/browser_plugin_post_message_guest.html
new file mode 100644
index 0000000000000000000000000000000000000000..57c1c3c452c800535a6c6bfafc063bd1002e3fd3
--- /dev/null
+++ b/content/test/data/browser_plugin_post_message_guest.html
@@ -0,0 +1,23 @@
+<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, '*');

[Charlie Reis, 2012/10/12 00:31:43]

Hmm, the window.name stuff is only useful on the iframe case so far, right? 
(Eventually, I think we want assigning a name to the browser plugin object to
show up in window.name of the guest, but that hasn't happened yet.)

It's confusing at the moment, but I suppose it's ok.

[Fady Samuel, 2012/10/12 18:07:53]

Sure, I'll work on that next.

+      }
+    }
+  }
+  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>