Make Sky example game run offline

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"];
+    _imgNebula = images["assets/nebula.png"];
 
     _gameLayer = new Node();
     this.addChild(_gameLayer);
 
     // Add some asteroids to the game world
     for (int i = 0; i < 5; i++) {
       addAsteroid(AsteroidSize.large);
     }
     for (int i = 0; i < 5; i++) {
       addAsteroid(AsteroidSize.medium);
     }
 
     // Add ship
     addShip();
 
     // Add background
-    Sprite sprtBackground = new Sprite.fromImage(images["res/starfield.png"]);
+    Sprite sprtBackground = new Sprite.fromImage(images["assets/starfield.png"]);
     sprtBackground.position = new Point(512.0, 512.0);
     sprtBackground.zPosition = -3.0;
     addChild(sprtBackground);
 
     // Add starfield
     _starField = new StarField(_spriteSheet, _numStarsInStarField);
     _starField.zPosition = -2.0;
     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"]);
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   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;
   }
 }