Update Button to be made of Material

sky/framework/components/menu_item.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 '../fn.dart';
 import 'button_base.dart';
 import 'icon.dart';
 import 'material.dart';
 
 class MenuItem extends ButtonBase {
@@ skipping 25 matching lines @@
       flex: 1;'''
   );
 
   List<Node> children;
   String icon;
 
   MenuItem({ Object key, this.icon, this.children }) : super(key: key);
 
   Node build() {
     return new Material (
-      style: highlight ? _highlightStyle : _style,
+      styles: [highlight ? _highlightStyle : _style],
       children: [
         new Icon(
-          style: _iconStyle,
+          styles: [_iconStyle],
           size: 24,
           type: "${icon}_grey600"
         ),
         new Container(
-          style: _labelStyle,
+          styles: [_labelStyle],
           children: children
         )
       ]
     );
   }
 }