Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia co…

sky/examples/game/lib/game_demo_world.dart

Index: sky/examples/game/lib/game_demo_world.dart
diff --git a/sky/examples/game/lib/game_demo_world.dart b/sky/examples/game/lib/game_demo_world.dart
index 605a08faaee62f4cff8d5001fda4c7971e2f7f17..4a70d39ee47b211bef880c0a3cb31d1081411eee 100644
--- a/sky/examples/game/lib/game_demo_world.dart
+++ b/sky/examples/game/lib/game_demo_world.dart
@@ -387,7 +387,7 @@ class StarField extends Node {
     }
   }
 
-  void paint(PictureRecorder canvas) {
+  void paint(RenderCanvas canvas) {
     // Setup paint object for opacity and transfer mode
     Paint paint = new Paint();
     paint.setTransferMode(TransferMode.plus);