Use StyleNode in StockMenu

sky/framework/components/popup_menu.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 'animated_component.dart';
 import '../animation/animated_value.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
 import '../theme/view-configuration.dart';
 import 'dart:math' as math;
@@ skipping 19 matching lines @@
     // TODO(abarth): We shouldn't mark the menu as closed until the animation
     // completes.
     isOpen = false;
   }
 }
 
 class PopupMenu extends AnimatedComponent {
   static final Style _style = new Style('''
     border-radius: 2px;
     padding: 8px 0;
-    background-color: ${Grey[50]};'''
-  );
+    box-sizing: border-box;
+    background-color: ${Grey[50]};''');
 
   List<List<Node>> items;
   int level;
   PopupMenuController controller;
 
   double _position;
   List<AnimatedValue> _opacities;
   int _width;
   int _height;
 
@@ skipping 47 matching lines @@
     }
 
     return new Material(
       style: _style,
       inlineStyle: _inlineStyle(),
       children: children,
       level: level
     );
   }
 }