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

sky/sdk/lib/rendering/stack.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:math' as math;
 
 import 'box.dart';
 import 'object.dart';
 
 class StackParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
@@ skipping 175 matching lines @@
       }
 
       child = parentData.nextSibling;
     }
   }
 
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
-  void paint(RenderObjectDisplayList canvas) {
+  void paint(RenderCanvas canvas) {
     defaultPaint(canvas);
   }
 }