Add the floating action button to stocks2

sky/sdk/lib/framework/rendering/box.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 'dart:sky' as sky;
 import 'dart:typed_data';
 import 'object.dart';
 import 'package:vector_math/vector_math.dart';
 import 'package:sky/framework/net/image_cache.dart' as image_cache;
@@ skipping 648 matching lines @@
     return paint;
   }
 
   void paint(RenderObjectDisplayList canvas) {
     sky.Paint paint = _createShadowPaint(_shadow);
     canvas.drawRect(new sky.Rect.fromLTRB(0.0, 0.0, size.width, size.height), paint);
     super.paint(canvas);
   }
 }
 
-typedef void CustomPaintCallback(RenderObjectDisplayList canvas);
+typedef void CustomPaintCallback(sky.Canvas canvas);
 
 class RenderCustomPaint extends RenderProxyBox {
 
   RenderCustomPaint({
     CustomPaintCallback callback,
     RenderBox child
   }) : super(child) {
     assert(callback != null);
     _callback = callback;
   }
@@ skipping 113 matching lines @@
 
   void defaultPaint(RenderObjectDisplayList canvas) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position);
       child = child.parentData.nextSibling;
     }
   }
 }