[Layout] Put in some guards to prevent us from reintroducing 'display' properties into the CSS.

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 '../layout.dart';
 import 'button_base.dart';
 import 'icon.dart';
 import 'ink_well.dart';
 
 class MenuItem extends ButtonBase {
   static final Style _style = new Style('''
     align-items: center;
     height: 48px;
     -webkit-user-select: none;'''
   );
 
   static final Style _highlightStyle = new Style('''
     align-items: center;
     height: 48px;
     background: rgba(153, 153, 153, 0.4);
     -webkit-user-select: none;'''
   );
 
   static final Style _iconStyle = new Style('''
     padding: 0px 16px;'''
   );
 
   static final Style _labelStyle = new Style('''
-    padding: 0px 16px;
-    flex: 1;'''
+    padding: 0px 16px;'''
   );
 
+  static final FlexBoxParentData _labelFlex = new FlexBoxParentData()..flex = 1;
+
   List<UINode> children;
   String icon;
   GestureEventListener onGestureTap;
 
   MenuItem({ Object key, this.icon, this.children, this.onGestureTap }) : super(key: key);
 
   UINode buildContent() {
     return new EventListenerNode(
       new StyleNode(
         new InkWell(
           children: [
             new StyleNode(
               new Icon(
                 size: 24,
                 type: "${icon}_grey600"
               ),
               _iconStyle
             ),
-            new FlexContainer(
-              direction: FlexDirection.Row,
-              style: _labelStyle,
-              children: children
+            new ParentDataNode(
+              new FlexContainer(
+                direction: FlexDirection.Row,
+                style: _labelStyle,
+                children: children
+              ),
+              _labelFlex
             )
           ]
         ),
         highlight ? _highlightStyle : _style
       ),
       onGestureTap: onGestureTap
     );
   }
 }