Split layout2.dart into several files

sky/examples/raw/sector_layout.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 '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';
 
 const double kTwoPi = 2 * math.PI;
 
 double deg(double radians) => radians * 180.0 / math.PI;
 
 class SectorConstraints {
   const SectorConstraints({
     this.minDeltaRadius: 0.0,
     this.maxDeltaRadius: double.INFINITY,
     this.minDeltaTheta: 0.0,
@@ skipping 479 matching lines @@
   rootCircle.add(new RenderSolidColor(0xFF0000FF, desiredDeltaTheta: kTwoPi * 0.4));
   var stack = new RenderSectorSlice(padding: 2.0);
   stack.add(new RenderSolidColor(0xFFFFFF00, desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(0xFFFF9000, desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(0xFF00FF00));
   rootCircle.add(stack);
 
   var root = new RenderBoxToRenderSectorAdapter(innerRadius: 50.0, child: rootCircle);
   app = new AppView(root);
 }