Remove one more use of mirrors: Components now have to explicitly sync their fields.

sky/sdk/lib/framework/components2/icon_button.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 '../rendering/box.dart';
 import 'icon.dart';
 
 class IconButton extends Component {
 
   IconButton({ String icon: '', this.onGestureTap })
     : super(key: icon), icon = icon;
 
-  String icon;
-  GestureEventListener onGestureTap;
+  final String icon;
+  final GestureEventListener onGestureTap;
 
   UINode build() {
     return new EventListenerNode(
       new Padding(
         child: new Icon(type: icon, size: 24),
         padding: const EdgeDims.all(8.0)),
       onGestureTap: onGestureTap);
   }
 
 }