Move simple_render_tree into tests as render_flex

sky/sdk/lib/framework/layout2.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 'node.dart';
 import 'dart:sky' as sky;
 
 // ABSTRACT LAYOUT
 
 class ParentData {
@@ skipping 807 matching lines @@
       assert(child.parentData is BlockParentData);
       child = child.parentData.nextSibling;
     }
 
     return new BoxDimensions(width: outerWidth,
                              height: constraints.constrainHeight(outerHeight));
   }
 
   void performLayout() {
     assert(constraints is BoxConstraints);
-    size.width = constraints.constrainWidth(constraints.maxWidth);
-    assert(size.width < double.INFINITY);
+    double width = constraints.constrainWidth(constraints.maxWidth);
     double y = 0.0;
-    double innerWidth = size.width;
     RenderBox child = firstChild;
     while (child != null) {
-      child.layout(new BoxConstraints(minWidth: innerWidth, maxWidth: innerWidth), parentUsesSize: true);
+      child.layout(new BoxConstraints(minWidth: width, maxWidth: width), parentUsesSize: true);
       assert(child.parentData is BlockParentData);
       child.parentData.position = new sky.Point(0.0, y);
       y += child.size.height;
       child = child.parentData.nextSibling;
     }
-    size.height = constraints.constrainHeight(y);
+    size = new sky.Size(width, constraints.constrainHeight(y));
+    assert(size.width < double.INFINITY);
+    assert(size.height < double.INFINITY);
   }
 
   void hitTestChildren(HitTestResult result, { sky.Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(RenderNodeDisplayList canvas) {
     super.paint(canvas);
     defaultPaint(canvas);
   }
@@ skipping 139 matching lines @@
 
   void hitTestChildren(HitTestResult result, { double x, double y }) {
     // defaultHitTestChildren(result, x: x, y: y);
   }
 
   void paint(RenderNodeDisplayList canvas) {
     super.paint(canvas);
     _layoutRoot.paint(canvas);
   }
 }