anchor.diff:   * and creating HTML event handlers that navigate to a URL.
    */
   class Router {
  -  final Map<UrlPattern, Handler> _handlers;
  +  final LinkedHashMap<UrlPattern, Handler> _handlers;
     final bool useFragment;
     bool _listen = false;
   
  
positive.code:    * [History.supportsState].
     */
    Router({bool useFragment})
        : _handlers = new Map<UrlPattern, Handler>(),
          useFragment = (useFragment == null)
              ? !History.supportsState
              : useFragment;
  
    void addHandler(UrlPattern pattern, Handler handler) {
      _logger.finest('addHandler $pattern');
      _handlers[pattern] = handler;
  
negative.code:     }
      return matches.first;
    }
  
    /**
     * Finds a matching [UrlPattern] added with [addHandler], parses the path
     * and invokes the associated callback.
  