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

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 8d7cda7c7f9bb22632342088e2a6cc301f1e7f3a..eb46a07900be514fbb37acbb609fa709f92e72d9 100644
--- a/sky/framework/components/menu_item.dart
+++ b/sky/framework/components/menu_item.dart
@@ -27,10 +27,11 @@ class MenuItem extends ButtonBase {
   );
 
   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;
@@ -49,10 +50,13 @@ class MenuItem extends ButtonBase {
               ),
               _iconStyle
             ),
-            new FlexContainer(
-              direction: FlexDirection.Row,
-              style: _labelStyle,
-              children: children
+            new ParentDataNode(
+              new FlexContainer(
+                direction: FlexDirection.Row,
+                style: _labelStyle,
+                children: children
+              ),
+              _labelFlex
             )
           ]
         ),