anchor.diff:    }
   
     void _paintBackgroundColor(sky.Canvas canvas, Rect rect) {
  -    if (_decoration.backgroundColor != null || _decoration.boxShadow != null ||
  +    if (_decoration.backgroundColor != null ||
  +        _decoration.boxShadow != null ||
           _decoration.gradient != null) {
         switch (_decoration.shape) {
           case Shape.circle:
  
positive.code:     this.tileMode: sky.TileMode.clamp
    });
  
    String toString() =>
        'RadialGradient($center, $radius, $colors, $colorStops, $tileMode)';
  
    sky.Shader createShader() {
      return new sky.Gradient.radial(this.center, this.radius, this.colors,
                                     this.colorStops, this.tileMode);
    }
  
    final Point center;
    final double radius;
    final List<Color> colors;
    final List<double> colorStops;
    final sky.TileMode tileMode;
  }
  
  enum BackgroundFit { fill, contain, cover, none, scaleDown }
  
negative.code:   if (b == null)
      return a.scale(1.0 - t);
    return new BoxShadow(
      color: lerpColor(a.color, b.color, t),
      offset: lerpOffset(a.offset, b.offset, t),
      blur: lerpNum(a.blur, b.blur, t)
    );
  }
  
  List<BoxShadow> lerpListBoxShadow(List<BoxShadow> a, List<BoxShadow> b, double t) {
  