anchor.diff:  }
   
   class TraceSummary {
  +  final int numSymbols;
  +
     Map<String, TraceSymbol> _symbols = {};
     List _events = [];
     List<TraceSymbol> _stack = [];
     List<TraceSymbol> _topExclusive = [];
     List<TraceSymbol> _topInclusive = [];
  +  bool _marked = false;
  +  int _totalSamples = 0;
  +
  +  TraceSummary(this.numSymbols);
   
     void _processEventsFromFile(String name) {
       var file = new File(name);
  
positive.code:       }
      }
    }
  
  
    static const NUM_SYMBOLS = 10;
  
    void _findTopExclusive() {
      _topExclusive = _symbols.values.toList();
  
negative.code:       symbol = new TraceSymbol(name);
        _symbols[name] = symbol;
      }
      _stack.add(symbol);
      _marked = false;
    }
  
    void _processEnd(Map event) {
  