Add @override annotation to known overriden methods

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

 part of sprites;
 
 /// The super class of any [Node] that has a size.
 ///
 /// NodeWithSize adds the ability for a node to have a size and a pivot point.
 class NodeWithSize extends Node {
 
   /// Changing the size will affect the size of the rendering of the node.
   ///
   ///     myNode.size = new Size(1024.0, 1024.0);
@@ skipping 30 matching lines @@
   ///       canvas.restore();
   ///     }
   void applyTransformForPivot(PaintingCanvas canvas) {
     if (pivot.x != 0 || pivot.y != 0) {
       double pivotInPointsX = size.width * pivot.x;
       double pivotInPointsY = size.height * pivot.y;
       canvas.translate(-pivotInPointsX, -pivotInPointsY);
     }
   }
 
+  @override
   bool isPointInside (Point nodePoint) {
 
     double minX = -size.width * pivot.x;
     double minY = -size.height * pivot.y;
     double maxX = minX + size.width;
     double maxY = minY + size.height;
     return (nodePoint.x >= minX && nodePoint.x < maxX &&
             nodePoint.y >= minY && nodePoint.y < maxY);
   }
 }