Split layout2.dart into several files

sky/examples/raw/render_paragraph.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:sky';
 import 'package:sky/framework/app.dart';
-import 'package:sky/framework/layout2.dart';
+import 'package:sky/framework/rendering/render_box.dart';
+import 'package:sky/framework/rendering/render_node.dart';
+import 'package:sky/framework/rendering/render_flex.dart';
+import 'package:sky/framework/rendering/render_paragraph.dart';
 
 class RenderSolidColor extends RenderDecoratedBox {
   final Size desiredSize;
   final int backgroundColor;
 
   RenderSolidColor(int backgroundColor, { this.desiredSize: const Size.infinite() })
       : backgroundColor = backgroundColor,
         super(decoration: new BoxDecoration(backgroundColor: backgroundColor));
 
   Size getIntrinsicDimensions(BoxConstraints constraints) {
-    return constraints.constrain(new Size(desiredWidth, desiredHeight));
+    return constraints.constrain(desiredSize);
   }
 
   void performLayout() {
     size = constraints.constrain(desiredSize);
   }
 
   void handlePointer(PointerEvent event) {
     if (event.type == 'pointerdown')
       decoration = new BoxDecoration(backgroundColor: 0xFFFF0000);
     else if (event.type == 'pointerup')
@@ skipping 24 matching lines @@
 
   child = new RenderDecoratedBox(
     decoration: new BoxDecoration(backgroundColor: 0xFFFFFFFF),
     child: new RenderParagraph(text: meatyString, color: 0xFF009900)
   );
   flexRoot.add(child);
   child.parentData.flex = 1;
 
   app = new AppView(root);
 }