anchor.diff:  class GameStorage {
     static final _gameCountKey = 'gameCount';
  +  final dartlib.EventHandle _highScoreUpdated;
   
     final Storage _storage;
   
     GameStorage() :
  -    _storage = window.localStorage {
  -  }
  +    _storage = window.localStorage,
  +    _highScoreUpdated = new dartlib.EventHandle();
   
     int get gameCount => _getIntValue(_gameCountKey);
  +
  +  dartlib.EventRoot get highScoreUpdated => _highScoreUpdated;
   
     void recordState(GameState state) {
       assert(state != null);
  
positive.code:     final m = game.field.mineCount;
      final duration = game.duration.inMilliseconds;
  
      final key = "w$w-h$h-m$m";
  
      final currentScore = _getIntValue(key, null);
      if(currentScore == null || currentScore > duration) {
        _setIntValue(key, duration);
        return true;
      } else {
        return false;
      }
    }
  
    void reset() {
  
negative.code:     _setIntValue(key, value + 1);
    }
  
    static String _getKey(int w, int h, int m) => "w$w-h$h-m$m";
  
  }
  