@Override
 public void buildContextMenu(ContextMenu menu, Context context, ContextMenuParams params) {
   mPopulator.buildContextMenu(menu, context, params);
   RewindableIterator<TabObserver> observers = mTab.getTabObservers();
   while (observers.hasNext()) {
     observers.next().onContextMenuShown(mTab, menu);
   }
 }
 @Override
 public boolean onItemSelected(ContextMenuHelper helper, ContextMenuParams params, int itemId) {
   return mPopulator.onItemSelected(helper, params, itemId);
 }