Enable setting the UINode key for ParentDataNodes

sky/sdk/lib/framework/fn2.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.
 
 library fn;
 
 import 'app.dart';
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
@@ skipping 136 matching lines @@
     node.setParent(this);
     node._sync(oldNode, slot);
     assert(node.root is RenderObject);
     return node;
   }
 }
 
 abstract class ContentNode extends UINode {
   UINode content;
 
-  ContentNode(UINode content) : this.content = content, super(key: content._key);
+  ContentNode(UINode content, { Object key }) : this.content = content, super(key: key);
 
   void _sync(UINode old, dynamic slot) {
     UINode oldContent = old == null ? null : (old as ContentNode).content;
     content = syncChild(content, oldContent, slot);
     assert(content.root != null);
     root = content.root;
   }
 
   void remove() {
     if (content != null)
       removeChild(content);
     super.remove();
   }
 }
 
 class ParentDataNode extends ContentNode {
   final ParentData parentData;
 
-  ParentDataNode(UINode content, this.parentData): super(content);
+  ParentDataNode(UINode content, this.parentData, { Object key }): super(content, key: key);
 }
 
 typedef void GestureEventListener(sky.GestureEvent e);
 typedef void PointerEventListener(sky.PointerEvent e);
 typedef void EventListener(sky.Event e);
 
 class EventListenerNode extends ContentNode  {
   final Map<String, sky.EventListener> listeners;
 
   static Map<String, sky.EventListener> _createListeners({
@@ skipping 560 matching lines @@
   }) : super(key: key, children: children);
 
   void syncRenderObject(UINode old) {
     super.syncRenderObject(old);
     root.direction = direction;
     root.justifyContent = justifyContent;
   }
 }
 
 class FlexExpandingChild extends ParentDataNode {
-  FlexExpandingChild(UINode content, [int flex = 1])
-    : super(content, new FlexBoxParentData()..flex = flex);
+  FlexExpandingChild(UINode content, { int flex: 1, Object key })
+    : super(content, new FlexBoxParentData()..flex = flex, key: key);
 }
 
 class Image extends RenderObjectWrapper {
   RenderImage root;
   RenderImage createNode() => new RenderImage(this.src, this.size);
 
   final String src;
   final Size size;
 
   Image({
@@ skipping 291 matching lines @@
     assert(root.parent is RenderView);
   }
 }
 
 class Text extends Component {
   Text(this.data) : super(key: '*text*');
   final String data;
   bool get interchangeable => true;
   UINode build() => new Paragraph(text: data);
 }