Fix Asteroids game to paint again and give it an icon.

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

 part of sprites;
 
 /// Options for setting up a [SpriteBox].
 ///
 ///  * [nativePoints], use the same points as the parent [Widget].
 ///  * [letterbox], use the size of the root node for the coordinate system, constrain the aspect ratio and trim off
 ///  areas that end up outside the screen.
 ///  * [stretch], use the size of the root node for the coordinate system, scale it to fit the size of the box.
 ///  * [scaleToFit], similar to the letterbox option, but instead of trimming areas the sprite system will be scaled
 ///  down to fit the box.
@@ skipping 270 matching lines @@
     _numFrames += 1;
 
     _frameRate = 1.0/delta;
 
     // Print frame rate
     if (_numFrames % 60 == 0) print("delta: $delta fps: $_frameRate");
 
     _runActions(_rootNode, delta);
     _callUpdate(_rootNode, delta);
     _scheduleTick();
+    markNeedsPaint();

[abarth-chromium, 2015/07/10 20:24:54]

Should should already be in the tree

   }
 
   void _runActions(Node node, double dt) {
     if (node._actions != null) {
       node._actions.step(dt);
     }
     for (int i = node.children.length - 1; i >= 0; i--) {
       Node child = node.children[i];
       _runActions(child, dt);
     }
@@ skipping 82 matching lines @@
   ///     if (event.pointer == firstPointerId) {
   ///       // Do something
   ///     }
   final int pointer;
 
   /// Creates a new SpriteBoxEvent, typically this is done internally inside the SpriteBox.
   ///
   ///     var event = new SpriteBoxEvent(new Point(50.0, 50.0), 'pointerdown', 0);
   SpriteBoxEvent(this.boxPosition, this.type, this.pointer);
 }