void Clear()
 {
   for (Content::iterator it = content_.begin();
        it != content_.end(); ++it)
   {
     delete *it;
   }
 }
    Content::iterator Find(const std::string& filename)
    {
      for (Content::iterator it = content_.begin();
           it != content_.end(); ++it)
      {
        if ((*it)->GetFilename() == filename)
        {
          return it;
        }
      }

      return content_.end();
    }