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

sky/examples/raw/spinning_arabic.dart

Index: sky/examples/raw/spinning_arabic.dart
diff --git a/sky/examples/raw/spinning_arabic.dart b/sky/examples/raw/spinning_arabic.dart
index 846aa2a4cb62d7e7295f4498105c7dd820ebc663..cc19a012c7110ae33d33bd80ccf9865f654cb190 100644
--- a/sky/examples/raw/spinning_arabic.dart
+++ b/sky/examples/raw/spinning_arabic.dart
@@ -12,7 +12,8 @@ void beginFrame(double timeStamp) {
   if (timeBase == null)
     timeBase = timeStamp;
   double delta = timeStamp - timeBase;
-  PictureRecorder canvas = new PictureRecorder(view.width, view.height);
+  PictureRecorder recorder = new PictureRecorder();
+  Canvas canvas = recorder.beginRecording(view.width, view.height);
   canvas.translate(view.width / 2.0, view.height / 2.0);
   canvas.rotate(math.PI * delta / 1800);
   canvas.drawRect(new Rect.fromLTRB(-100.0, -100.0, 100.0, 100.0),
@@ -25,7 +26,7 @@ void beginFrame(double timeStamp) {
   canvas.translate(layoutRoot.maxWidth / -2.0, (layoutRoot.maxWidth / 2.0) - 125);
   layoutRoot.paint(canvas);
 
-  view.picture = canvas.endRecording();
+  view.picture = recorder.endRecording();
   view.scheduleFrame();
 }