Add @override annotation to known overriden methods

sky/sdk/example/game/lib/sprite.dart

 part of sprites;
 
 /// A Sprite is a [Node] that renders a bitmap image to the screen.
 class Sprite extends NodeWithSize {
 
   /// The texture that the sprite will render to screen.
   ///
   /// If the texture is null, the sprite will be rendered as a red square
   /// marking the bounds of the sprite.
   ///
@@ skipping 46 matching lines @@
   ///
   ///     mySprite.opacity = 0.5;
   double get opacity => _opacity;
 
   void set opacity(double opacity) {
     assert(opacity != null);
     assert(opacity >= 0.0 && opacity <= 1.0);
     _opacity = opacity;
   }
 
+  @override
   void paint(PaintingCanvas canvas) {
     canvas.save();
 
     // Account for pivot point
     applyTransformForPivot(canvas);
 
     if (texture != null) {
       double w = texture.size.width;
       double h = texture.size.height;
 
       if (w <= 0 || h <= 0) return;
-      
+
       double scaleX = size.width / w;
       double scaleY = size.height / h;
-      
+
       if (constrainProportions) {
         // Constrain proportions, using the smallest scale and by centering the image
         if (scaleX < scaleY) {
           canvas.translate(0.0, (size.height - scaleX * h) / 2.0);
           scaleY = scaleX;
         } else {
           canvas.translate((size.width - scaleY * w) / 2.0, 0.0);
           scaleX = scaleY;
         }
       }
-      
+
       canvas.scale(scaleX, scaleY);
 
       // Setup paint object for opacity and transfer mode
       Paint paint = new Paint();
       paint.color = new Color.fromARGB((255.0*_opacity).toInt(), 255, 255, 255);
       if (colorOverlay != null) {
         paint.setColorFilter(new ColorFilter.mode(colorOverlay, TransferMode.srcATop));
       }
       if (transferMode != null) {
         paint.setTransferMode(transferMode);
       }
 
       // Do actual drawing of the sprite
       texture.drawTexture(canvas, Point.origin, paint);
     } else {
       // Paint a red square for missing texture
       canvas.drawRect(new Rect.fromLTRB(0.0, 0.0, size.width, size.height),
       new Paint()..color = const Color.fromARGB(255, 255, 0, 0));
     }
     canvas.restore();
   }
 }