Give RenderObject a useful toString().

sky/sdk/lib/framework/components2/scaffold.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 '../fn2.dart';
 import 'dart:sky' as sky;
 import '../rendering/box.dart';
 import '../rendering/object.dart';
 
 
@@ skipping 112 matching lines @@
       if (box != null) {
         assert(box.parentData is BoxParentData);
         if (new sky.Rect.fromPointAndSize(box.parentData.position, box.size).contains(position)) {
           if (box.hitTest(result, position: (position - box.parentData.position).toPoint()))
             return;
         }
       }
     }
   }
 
+  String debugDescribeChildren(String prefix) {
+    return _slots.keys.map((slot) => '${prefix}${slot}: ${_slots[slot].toString(prefix)}').join('\n');
+  }
 }
 
 class Scaffold extends RenderObjectWrapper {
 
   // static final Style _style = new Style('''
   //   ${typography.typeface};
   //   ${typography.black.body1};''');
 
   Scaffold({
     Object key,
@@ skipping 28 matching lines @@
   void syncRenderObject(UINode old) {
     super.syncRenderObject(old);
     syncChild(toolbar, old is Scaffold ? old.toolbar : null, ScaffoldSlots.toolbar);
     syncChild(body, old is Scaffold ? old.body : null, ScaffoldSlots.body);
     syncChild(statusbar, old is Scaffold ? old.statusbar : null, ScaffoldSlots.statusBar);
     syncChild(drawer, old is Scaffold ? old.drawer : null, ScaffoldSlots.drawer);
     syncChild(floatingActionButton, old is Scaffold ? old.floatingActionButton : null, ScaffoldSlots.floatingActionButton);
   }
 
 }