Give RenderObject a useful toString().

sky/sdk/lib/framework/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:sky' as sky;
 import 'box.dart';
 import 'object.dart';
 
 class FlexBoxParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
   int flex;
   void merge(FlexBoxParentData other) {
     if (other.flex != null)
       flex = other.flex;
     super.merge(other);
   }
+  String toString() => '${super.toString()}; flex=$flex';
 }
 
 enum FlexDirection { horizontal, vertical }
 
 class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, FlexBoxParentData>,
                                         RenderBoxContainerDefaultsMixin<RenderBox, FlexBoxParentData> {
   // lays out RenderBox children using flexible layout
 
   RenderFlex({
     FlexDirection direction: FlexDirection.horizontal
@@ skipping 85 matching lines @@
   }
 
   void hitTestChildren(HitTestResult result, { sky.Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(RenderObjectDisplayList canvas) {
     defaultPaint(canvas);
   }
 }