Browser Plugin: Implement CanGoBack/CanGoForward

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;
   }
 }
 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() {
   var plugin = document.getElementById('plugin');
   plugin.back();
 }
+function CanGoBack() {
+  var plugin = document.getElementById('plugin');
+  return plugin.canGoBack();
+}
+function CanGoForward() {
+  var plugin = document.getElementById('plugin');
+  return plugin.canGoForward();
+}
 function Forward() {
   var plugin = document.getElementById('plugin');
   plugin.forward();
 }
 function Go(relativeIndex) {
   var plugin = document.getElementById('plugin');
   plugin.go(relativeIndex);
 }
 function SetTitle(str) {
   document.title = str;
 }
 document.title = 'embedder';
 </script>
 
 <object id="plugin"
     tabindex="0"
     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);
 </script>