Make UINode's key a String

sky/sdk/lib/widgets/radio.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 '../rendering/object.dart';
 import '../theme2/colors.dart' as colors;
 import 'basic.dart';
 import 'button_base.dart';
 
 typedef void ValueChanged(value);
 
 class Radio extends ButtonBase {
 
   Radio({
-    Object key,
+    String key,
     this.value,
     this.groupValue,
     this.onChanged
   }) : super(key: key);
 
   Object value;
   Object groupValue;
   ValueChanged onChanged;
 
   void syncFields(Radio source) {
@@ skipping 34 matching lines @@
       ),
       onGestureTap: _handleClick
     );
   }
 
   void _handleClick(_) {
     onChanged(value);
   }
 
 }