anchor.diff:    Image(int width, int height, [this._format = RGBA]) :
       this.width = width,
       this.height = height,
  -    _data = new Uint32List(width * height);
  +    data = new Uint32List(width * height);
   
     /**
      * Create a copy of the image [other].
  
positive.code:    */
    void setPixel(int x, int y, int color) {
      if (boundsSafe(x, y)) {
        _data[y * width + x] = color;
      }
    }
  
  
negative.code:   /**
     * The size of the image buffer.
     */
    int get length => data.length;
  
    /**
     * Get a pixel from the buffer.
     */
    int operator[](int index) => data[index];
  
    /**
     * Set a pixel in the buffer.
     */
    void operator[]=(int index, int color) {
      data[index] = color;
    }
  
    /**
  