Make RenderFlex support taking children in the constructor.

sky/sdk/lib/rendering/flex.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 'box.dart';
 import 'object.dart';
 
 class FlexBoxParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
@@ skipping 24 matching lines @@
   center,
 }
 
 typedef double _ChildSizingFunction(RenderBox child, BoxConstraints constraints);
 
 class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, FlexBoxParentData>,
                                         RenderBoxContainerDefaultsMixin<RenderBox, FlexBoxParentData> {
   // lays out RenderBox children using flexible layout
 
   RenderFlex({
+    List<RenderBox> children,
     FlexDirection direction: FlexDirection.horizontal,
     FlexJustifyContent justifyContent: FlexJustifyContent.start,
     FlexAlignItems alignItems: FlexAlignItems.center
-  }) : _direction = direction, _justifyContent = justifyContent, _alignItems = alignItems;
+    }) : _direction = direction,
+         _justifyContent = justifyContent,
+         _alignItems = alignItems {
+      addAll(children);
+    }
+
 
   FlexDirection _direction;
   FlexDirection get direction => _direction;
   void set direction (FlexDirection value) {
     if (_direction != value) {
       _direction = value;
       markNeedsLayout();
     }
   }
 
@@ skipping 331 matching lines @@
   }
 
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(PaintingCanvas canvas, Offset offset) {
     defaultPaint(canvas, offset);
   }
 }