anchor.diff:      return new QrDemo._internal(canvas);
     }
   
  -  QrDemo._internal(this._canvas) {
  +  QrDemo._internal(this._canvas)
  +  : _squares = new List<bool>() {
       _canvas.on.mouseMove.add(_canvas_mouseMove);
       _canvas.on.mouseOut.add(_canvas_mouseOut);
     }
  
positive.code: 
    void _setMouse(core.Coordinate value) {
      _mouseLocation = value;
      requestFrame();
    }
  }
  
negative.code: main(){
    CanvasElement canvas = document.query("#content");
    final demo = new QrDemo(canvas);
    demo._setValue("hello world");
    demo.requestFrame();
  }
  
  class QrDemo{
    static final int typeNumber = 10;
    static final int size = typeNumber * 4 + 17;
    static final int scale = 5;
  
    final List<bool> _squares;
  
    final CanvasElement _canvas;
    CanvasRenderingContext2D _ctx;
  
    core.Coordinate _mouseLocation;
    bool _frameRequested = false;
  