Re-work MaterialComponent

sky/framework/components/menu_item.dart

Index: sky/framework/components/menu_item.dart
diff --git a/sky/framework/components/menu_item.dart b/sky/framework/components/menu_item.dart
index dc1b8dfe165e2408944aa1852648606514fe03dc..4db0d001656a922c123985012f13ccbf6cc7dd44 100644
--- a/sky/framework/components/menu_item.dart
+++ b/sky/framework/components/menu_item.dart
@@ -5,6 +5,7 @@
 import '../fn.dart';
 import 'button_base.dart';
 import 'icon.dart';
+import 'material.dart';
 
 class MenuItem extends ButtonBase {
   static final Style _style = new Style('''
@@ -41,10 +42,9 @@ class MenuItem extends ButtonBase {
   MenuItem({ Object key, this.icon, this.children }) : super(key: key);
 
   Node build() {
-    return new Container(
+    return new Material (
       style: highlight ? _highlightStyle : _style,
       children: [
-        super.build(),
         new Icon(
           style: _iconStyle,
           size: 24,