anchor.diff:  }
   
   class HistoryEntry {
  -  HistoryEntry(this.route);
  +  HistoryEntry({ this.route, this.key });
     final RouteBase route;
  +  final int key;
     // TODO(jackson): Keep track of the requested transition
   }
   
  
positive.code:       if (route.name != null)
          namedRoutes[route.name] = route;
      }
      history.add(new HistoryEntry(routes[0]));
    }
  
    List<HistoryEntry> history = new List<HistoryEntry>();
    int historyIndex = 0;
    Map<String, RouteBase> namedRoutes = new Map<String, RouteBase>();
  
    RouteBase get currentRoute => history[historyIndex].route;
  
negative.code:   }
  
    void push(RouteBase route) {
      HistoryEntry historyEntry = new HistoryEntry(route: route, key: _lastKey++);
      history.insert(historyIndex + 1, historyEntry);
      historyIndex++;
    }
  