Clean up a bunch of our Dart code.

sky/sdk/lib/framework/components2/button_base.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';
 
 abstract class ButtonBase extends Component {
-  bool highlight = false;
 
   ButtonBase({ Object key }) : super(key: key);
 
   UINode buildContent();
 
   UINode build() {
     return new EventListenerNode(
       buildContent(),
       onPointerDown: _handlePointerDown,
       onPointerUp: _handlePointerUp,
       onPointerCancel: _handlePointerCancel
     );
   }
 
+  bool highlight = false;
+
   void _handlePointerDown(_) {
     setState(() {
       highlight = true;
     });
   }
   void _handlePointerUp(_) {
     setState(() {
       highlight = false;
     });
   }
   void _handlePointerCancel(_) {
     setState(() {
       highlight = false;
     });
   }
 }