Browser plugin: Implement loadStart and loadAbort events

content/test/data/browser_plugin_embedder.html

 <script type="text/javascript">
+var url;

[Charlie Reis, 2012/10/03 01:52:30]

nit: loadStartUrl
That will make the test more obvious, and leave this flexible for other event
listeners.

[Fady Samuel, 2012/10/04 00:43:38]

Done.

+function loadStart(event) {
+  url = event.url;
+}
 function SetSrc(src) {
   var plugin = document.getElementById('plugin');
   plugin.src = src;
+  plugin.addEventListener('loadStart', loadStart);
 }
 function SetSize(w, h) {
   var plugin = document.getElementById('plugin');
   plugin.width = w;
   plugin.height = h;
 }
 function Back() {
   var plugin = document.getElementById('plugin');
   plugin.back();
 }
 function Forward() {
   var plugin = document.getElementById('plugin');
   plugin.forward();
 }
 function Go(relativeIndex) {
   var plugin = document.getElementById('plugin');
   plugin.go(relativeIndex);
 }
+

[Charlie Reis, 2012/10/03 01:52:30]

nit: Remove.  (No need for extra code churn.)

[Fady Samuel, 2012/10/04 00:43:38]

Done.

 </script>
 
 <object id="plugin"
     tabindex="0"
     type="application/new-browser-plugin"
     width="640"
     height="480"
     border="0px"></object>