Enable setting the UINode key for ParentDataNodes

sky/sdk/lib/framework/components2/menu_item.dart

Index: sky/sdk/lib/framework/components2/menu_item.dart
diff --git a/sky/sdk/lib/framework/components2/menu_item.dart b/sky/sdk/lib/framework/components2/menu_item.dart
index bf47b4d31d56267516d0ea194aa8dfe0ff7c2d9f..e3487edc2ae6ed55976276a47cbd9a9990b5e206 100644
--- a/sky/sdk/lib/framework/components2/menu_item.dart
+++ b/sky/sdk/lib/framework/components2/menu_item.dart
@@ -11,7 +11,7 @@ class MenuItem extends ButtonBase {
 
   static const BoxDecoration highlightDecoration = const BoxDecoration(
     backgroundColor: const Color.fromARGB(102, 153, 153, 153)
-  ); 
+  );
 
   List<UINode> children;
   String icon;
@@ -36,7 +36,7 @@ class MenuItem extends ButtonBase {
                 ),
                 padding: const EdgeDims.symmetric(horizontal: 16.0)
               ),
-              1
+              flex: 1
             )
           ]
         ),