Browser Plugin: Implement Back, Forward, and Go.

content/test/data/browser_plugin_embedder.html

 <script type="text/javascript">
 function SetSrc(src) {
-  plugin = document.getElementById('plugin');
+  var plugin = document.getElementById('plugin');
   plugin.src = src;
 }
 function SetSize(w, h) {
-  plugin = document.getElementById('plugin');
+  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);
+}
 </script>
 
 <object id="plugin"
     tabindex="0"
     type="application/new-browser-plugin"
     width="640"
     height="480"
     border="0px"></object>