Make the menu items in the drawer change colour when tapped, per Material spec.

sky/sdk/lib/widgets/default_text_style.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 '../painting/text_style.dart';
 import 'basic.dart';
 import 'widget.dart';
 
 class DefaultTextStyle extends Inherited {
 
   DefaultTextStyle({
     String key,
     this.style,
     Widget child
   }) : super(key: key, child: child) {
     assert(style != null);
     assert(child != null);
   }
 
   final TextStyle style;
 
   static TextStyle of(Component component) {
     DefaultTextStyle result = component.inheritedOfType(DefaultTextStyle);
     return result == null ? null : result.style;
   }
+
+  bool syncShouldNotify(DefaultTextStyle old) => style != old.style;
+
 }