Browser plugin: Implement titleChanged event.

content/test/data/browser_plugin_embedder.html

 <script type="text/javascript">
 function loadAbort(evt) {
   document.title = evt.type;
 }
 function loadStart(evt) {
   document.title = evt.url;
 }
 var redirectOldUrl;
 var redirectNewUrl;
 function loadRedirect(event) {
   document.title = "redirected";
   if (event.isTopLevel) {
     redirectOldUrl = event.oldUrl;
     redirectNewUrl = event.newUrl;
   }
 }
+var shouldEchoTitle = false;
+function titleChanged(evt) {
+  if (shouldEchoTitle)
+    document.title = evt.title;
+}
 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;
 }
 function Back() {
@@ skipping 19 matching lines @@
     type="application/browser-plugin"
     width="640"
     height="480"
     border="0px"></object>
 
 <script>
   var plugin = document.getElementById('plugin');
   plugin.addEventListener('loadStart', loadStart);
   plugin.addEventListener('loadAbort', loadAbort);
   plugin.addEventListener('loadRedirect', loadRedirect);
+  plugin.addEventListener('titleChanged', titleChanged);
 </script>