Make UINode's key a String

sky/sdk/lib/widgets/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 '../rendering/box.dart';
 import '../rendering/object.dart';
 import '../theme2/view_configuration.dart';
 import 'ui_node.dart';
 
 enum ScaffoldSlots {
@@ skipping 141 matching lines @@
   }
 }
 
 class Scaffold extends RenderObjectWrapper {
 
   // static final Style _style = new Style('''
   //   ${typography.typeface};
   //   ${typography.black.body1};''');
 
   Scaffold({
-    Object key,
+    String key,
     UINode toolbar,
     UINode body,
     UINode statusBar,
     UINode drawer,
     UINode floatingActionButton
   }) : _toolbar = toolbar,
        _body = body,
        _statusBar = statusBar,
        _drawer = drawer,
        _floatingActionButton = floatingActionButton,
        super(key: key);
 
   UINode _toolbar;
   UINode _body;
   UINode _statusBar;
   UINode _drawer;
   UINode _floatingActionButton;
 
-  RenderScaffold get root { RenderScaffold result = super.root; return result; }
+  RenderScaffold get root => super.root;
   RenderScaffold createNode() => new RenderScaffold();
 
   void insert(RenderObjectWrapper child, ScaffoldSlots slot) {
     root[slot] = child != null ? child.root : null;
   }
 
   void removeChild(UINode node) {
     assert(node != null);
     root.remove(node.root);
     super.removeChild(node);
@@ skipping 16 matching lines @@
   void syncRenderObject(UINode old) {
     super.syncRenderObject(old);
     _toolbar = syncChild(_toolbar, old is Scaffold ? old._toolbar : null, ScaffoldSlots.toolbar);
     _body = syncChild(_body, old is Scaffold ? old._body : null, ScaffoldSlots.body);
     _statusBar = syncChild(_statusBar, old is Scaffold ? old._statusBar : null, ScaffoldSlots.statusBar);
     _drawer = syncChild(_drawer, old is Scaffold ? old._drawer : null, ScaffoldSlots.drawer);
     _floatingActionButton = syncChild(_floatingActionButton, old is Scaffold ? old._floatingActionButton : null, ScaffoldSlots.floatingActionButton);
   }
 
 }