Rename BlockContainer, StackContainer, and FlexContainer

sky/sdk/lib/framework/components2/fixed_height_scrollable.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 '../animation/scroll_behavior.dart';
 import '../fn2.dart';
 import 'dart:async';
 import 'dart:math' as math;
 import 'package:vector_math/vector_math.dart';
 import 'scrollable.dart';
@@ skipping 57 matching lines @@
 
     return new SizeObserver(
       callback: _handleSizeChanged,
       child: new Clip(
         child: new DecoratedBox(
           decoration: const BoxDecoration(
             backgroundColor: const Color(0xFFFFFFFF)
           ),
           child: new Transform(
             transform: transform,
-            child: new BlockContainer(
-              children: buildItems(itemShowIndex, itemShowCount))
+            child: new Block(buildItems(itemShowIndex, itemShowCount))
           )
         )
       )
     );
   }
 
   List<UINode> buildItems(int start, int count);  
 
 }