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

sky/examples/raw/hello_world.dart

Index: sky/examples/raw/hello_world.dart
diff --git a/sky/examples/raw/hello_world.dart b/sky/examples/raw/hello_world.dart
index 4264abf8990f0bee5c78ce2d5bad6f70456e9ee3..8b77e90a674e7e240a251cb43d890b82169a6bcc 100644
--- a/sky/examples/raw/hello_world.dart
+++ b/sky/examples/raw/hello_world.dart
@@ -9,11 +9,12 @@ Picture draw(int a, int r, int g, int b) {
   double width = view.width;
   double height = view.height;
 
-  PictureRecorder recorder = new PictureRecorder(width, height);
+  PictureRecorder recorder = new PictureRecorder();
+  Canvas canvas = recorder.beginRecording(width, height);
   double radius = min(width, height) * 0.45;
 
   Paint paint = new Paint()..color = new Color.fromARGB(a, r, g, b);
-  recorder.drawCircle(width / 2, height / 2, radius, paint);
+  canvas.drawCircle(width / 2, height / 2, radius, paint);
   return recorder.endRecording();
 }