Add BlockContainer to fn2

sky/sdk/lib/framework/fn2.dart

Index: sky/sdk/lib/framework/fn2.dart
diff --git a/sky/sdk/lib/framework/fn2.dart b/sky/sdk/lib/framework/fn2.dart
index 15dce299a68d4a5bd8bfaf927ed88be7c364f666..72b84ce8766887f9c3e9386feafb5c5d3a725c91 100644
--- a/sky/sdk/lib/framework/fn2.dart
+++ b/sky/sdk/lib/framework/fn2.dart
@@ -501,16 +501,16 @@ abstract class OneChildListRenderNodeWrapper extends RenderNodeWrapper {
   }
 }
 
-class Container extends OneChildListRenderNodeWrapper {
+class BlockContainer extends OneChildListRenderNodeWrapper {
 
-  RenderCSSContainer root;
-  RenderCSSContainer createNode() => new RenderCSSContainer(this);
+  RenderBlock root;
+  RenderBlock createNode() => new RenderBlock();
 
-  static final Container _emptyContainer = new Container();
+  static final BlockContainer _emptyContainer = new BlockContainer();
 
   RenderNodeWrapper get emptyNode => _emptyContainer;
 
-  Container({
+  BlockContainer({
     Object key,
     List<UINode> children
   }) : super(