Split layout2.dart into several files

sky/sdk/lib/framework/fn2.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.
 
 library fn;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
 import 'dart:sky' as sky;
 import 'reflect.dart' as reflect;
-import 'layout2.dart';
 import 'app.dart';
+import 'rendering/render_block.dart';
+import 'rendering/render_box.dart';
+import 'rendering/render_flex.dart';
+import 'rendering/render_node.dart';
+import 'rendering/render_paragraph.dart';
 
 // final sky.Tracing _tracing = sky.window.tracing;
 
 final bool _shouldLogRenderDuration = false;
 final bool _shouldTrace = false;
 
 enum _SyncOperation { IDENTICAL, INSERTION, STATEFUL, STATELESS, REMOVAL }
 
 /*
  * All Effen nodes derive from UINode. All nodes have a _parent, a _key and
@@ skipping 934 matching lines @@
 
   final int color;
 
   RenderSolidColor root;
   RenderSolidColor createNode() => new RenderSolidColor(color, desiredSize: new sky.Size(40.0, 130.0));
 
   static final Rectangle _emptyRectangle = new Rectangle(0);
   RenderNodeWrapper get emptyNode => _emptyRectangle;
 
 }