anchor.diff:  class RequestNavigator {
     final Stream<HttpRequest> _incoming;
     final Router _router;
  -  final Map<String, StreamController<HttpRequest>> _streams = {};
  +  final Map<_ServerRoute, StreamController<HttpRequest>> _streams = {};
   
     /**
      * Contains [Route], [Filter], [Stream] triples where [Stream] has at least one handler.
      */
     final List _filters = [];
  +
  +  final _ServerRoute _defaultServerRouteId = new _ServerRoute('default', '');
   
     /**
      * Creates new RequestNavigator listening on [_incoming].
  
positive.code:    * Registers [Handler] for a [Route] and adds listener to the stream which
     * is also returned.
     */
    Stream<HttpRequest> registerHandler(String routeName, dynamic handler){
      if(routeName == 'default') {
        throw new ArgumentError("Route name should not be 'default'.");
      }
      if(_streams.containsKey(routeName)){
        throw new ArgumentError("Route name '$routeName' already in use in RequestNavigator.");
      }
  
      _streams[routeName] = _createStreamControllerWithHandler(handler);
      return _streams[routeName].stream;
    }
  
    /**
  
negative.code:   }
  
    Stream<HttpRequest> _navigateToRoute(HttpRequest req, String routeName, Map params){
      var serverRoute = new _ServerRoute(routeName, req.method);
  
      if(!_streams.containsKey(serverRoute)){
        throw new ArgumentError("Stream not found for '$serverRoute'");
      }
  
      var streamController = _streams[serverRoute];
      streamController.add(req);
      return streamController.stream;
    }
  