Refactor layout/relayout into a single method.

sky/examples/raw/simple_render_tree.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';
 
 class RenderSolidColor extends RenderDecoratedBox {
   final double desiredHeight;
   final double desiredWidth;
   final int backgroundColor;
 
   RenderSolidColor(int backgroundColor, { this.desiredHeight: double.INFINITY,
                                           this.desiredWidth: double.INFINITY })
       : backgroundColor = backgroundColor,
         super(new BoxDecoration(backgroundColor: backgroundColor));
 
   BoxDimensions getIntrinsicDimensions(BoxConstraints constraints) {
     return new BoxDimensions.withConstraints(constraints,
                                              height: desiredHeight,
                                              width: desiredWidth);
   }
 
-  void layout(BoxConstraints constraints, { RenderNode relayoutSubtreeRoot }) {
+  void performLayout() {
     width = constraints.constrainWidth(desiredWidth);
     height = constraints.constrainHeight(desiredHeight);
-    layoutDone();
   }
 
   void handlePointer(PointerEvent event) {
     if (event.type == 'pointerdown')
       decoration = new BoxDecoration(backgroundColor: 0xFFFF0000);
     else if (event.type == 'pointerup')
       decoration = new BoxDecoration(backgroundColor: backgroundColor);
   }
 }
 
@@ skipping 31 matching lines @@
   // Purple and blue cells
   addFlexChild(row, 0x77FF00FF, flex: 1);
   addFlexChild(row, 0xFF0000FF, flex: 2);
 
   root.add(row);
   row.parentData.flex = 3;
 
   app = new AppView(root);
 
 }