anchor.diff:  
     void draw(CanvasRenderingContext2D context) {
       context.clearRect(0, 0, canvas.width, canvas.height);
  -    _debugDraw(context);
  +    if (DEBUG) _debugDraw(context);
       currentScene.drawWithChildren(context);
     }
   
     void run([Scene scene]) {
  -    if (scene != null) {
  -      currentScene = scene;
  +    if (scene == null) {
  +      scene = new Scene();
       }
  -      var initTime;
  -      var frameCount = 0;
  +    currentScene = scene;
  +    
  +    var initTime;
  +    var frameCount = 0;
   
       drawFrame(num currentTime) {
         if (initTime == null) {
  
positive.code:     new Timer.periodic(new Duration(seconds:1), (t) {
        fps = frameCount;
        frameCount = 0;
        print('fps: $fps');
      });
    }
  }
  
negative.code: // limitations under the License.
  
  part of cocos;
  
  const DEBUG = false;
  
  class Game {
    AssetManager assets;
  