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

sky/sdk/lib/rendering/flex.dart

Index: sky/sdk/lib/rendering/flex.dart
diff --git a/sky/sdk/lib/rendering/flex.dart b/sky/sdk/lib/rendering/flex.dart
index 8b0c40981ff4a478b41b7bbee212cc9e188d5dc6..e883e51612b6cd1eb8177098dd9e213c9edde22f 100644
--- a/sky/sdk/lib/rendering/flex.dart
+++ b/sky/sdk/lib/rendering/flex.dart
@@ -381,7 +381,7 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     defaultHitTestChildren(result, position: position);
   }
 
-  void paint(RenderObjectDisplayList canvas) {
+  void paint(RenderCanvas canvas) {
     defaultPaint(canvas);
   }
 }