Add @override annotation to known overriden methods

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

 part of game;
 
 const double _steeringThreshold = 0.0;
 const double _steeringMax = 150.0;
 
 // Random generator
 Math.Random _rand = new Math.Random();
 
 const double _gameSizeWidth = 1024.0;
 const double _gameSizeHeight = 1024.0;
@@ skipping 29 matching lines @@
   Ship _ship;
   Sprite _shield;
   List<Asteroid> _asteroids = [];
   List<Laser> _lasers = [];
   StarField _starField;
   Nebula _nebula;
 
   // Game state
   int _numFrames = 0;
   bool _isGameOver = false;
-  
+
   GameDemoWorld(this._app, ImageMap images, this._spriteSheet) : super(new Size(_gameSizeWidth, _gameSizeHeight)) {
 
     // Fetch images
     _imgNebula = images["res/nebula.png"];
 
     _gameLayer = new Node();
     this.addChild(_gameLayer);
 
     // Add some asteroids to the game world
     for (int i = 0; i < 5; i++) {
@@ skipping 18 matching lines @@
     addChild(_starField);
 
     // Add nebula
     addNebula();
 
     userInteractionEnabled = true;
     handleMultiplePointers = true;
   }
 
   // Methods for adding game objects
-  
+
   void addAsteroid(AsteroidSize size, [Point pos]) {
     Asteroid asteroid = new Asteroid(_spriteSheet, size);
     asteroid.zPosition = 1.0;
     if (pos != null) asteroid.position = pos;
     _gameLayer.addChild(asteroid);
     _asteroids.add(asteroid);
   }
 
   void addShip() {
     Ship ship = new Ship(_spriteSheet["ship.png"]);
@@ skipping 97 matching lines @@
     explosionNode.position = position;
     explosionNode.zPosition = 1010.0;
 
     if (asteroidSize == AsteroidSize.large) {
       explosionNode.scale = 1.5;
     }
 
     _gameLayer.addChild(explosionNode);
   }
 
+  @override
   void update(double dt) {
     // Move asteroids
     for (Asteroid asteroid in _asteroids) {
       asteroid.position = pointAdd(asteroid.position, asteroid._movementVector);
     }
 
     // Move lasers and remove expired lasers
     for (int i = _lasers.length - 1; i >= 0; i--) {
       Laser laser = _lasers[i];
       laser.move();
@@ skipping 123 matching lines @@
 
     addLaser();
   }
 
   // Handle pointer events
 
   int _firstPointer = -1;
   int _secondPointer = -1;
   Point _firstPointerDownPos;
 
+  @override
   bool handleEvent(SpriteBoxEvent event) {
 
     Point pointerPos = convertPointToNodeSpace(event.boxPosition);
     int pointer = event.pointer;
 
     switch (event.type) {
       case 'pointerdown':
         if (_firstPointer == -1) {
           // Assign the first pointer
           _firstPointer = pointer;
@@ skipping 87 matching lines @@
 
     userInteractionEnabled = true;
 
     // Rotate forever
     double direction = (_rand.nextBool()) ? 360.0 : -360.0;
     ActionTween rot = new ActionTween( (a) => rotation = a, 0.0, direction, 2.0 * _rand.nextDouble() + 2.0);
     ActionRepeatForever repeat = new ActionRepeatForever(rot);
     actions.run(repeat);
   }
 
+  @override
   bool handleEvent(SpriteBoxEvent event) {
     if (event.type == "pointerdown") {
       actions.stopWithTag("fade");
       colorOverlay = new Color(0x99ffffff);
     }
     else if (event.type == "pointerup") {
       // Fade out the color overlay
       Action fadeOut = new ActionTween((a) => this.colorOverlay = a, new Color(0x99ffffff), new Color(0x00ffffff), 1.0);
       Action fadeOutAndRemove = new ActionSequence([fadeOut, new ActionCallFunction(() => this.colorOverlay = null)]);
       actions.run(fadeOutAndRemove, "fade");
@@ skipping 156 matching lines @@
   double dy = a.y - b.y;
   if (dx < 0.0) dx = -dx;
   if (dy < 0.0) dy = -dy;
   if (dx > dy) {
     return dx + dy/2.0;
   }
   else {
     return dy + dx/2.0;
   }
 }