Make the popup menu animation correct

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

Index: sky/sdk/lib/framework/components2/popup_menu_item.dart
diff --git a/sky/sdk/lib/framework/components2/popup_menu_item.dart b/sky/sdk/lib/framework/components2/popup_menu_item.dart
index d98e9f4d07b530a2ec3e9a56d09698ee072a03a5..78bb37f47bdc1f064a6f89d321c8f78258dfbd60 100644
--- a/sky/sdk/lib/framework/components2/popup_menu_item.dart
+++ b/sky/sdk/lib/framework/components2/popup_menu_item.dart
@@ -12,11 +12,15 @@ class PopupMenuItem extends Component {
   final double opacity;
 
   UINode build() {
-    return new Container(
-      constraints: const BoxConstraints(minWidth: 112.0),
-      padding: const EdgeDims.all(16.0),
-      // TODO(abarth): opacity: opacity,
-      child: new Flex(children)
+    return new Opacity(
+      opacity: opacity,
+      child: new InkWell(
+        children: [new Container(
+          constraints: const BoxConstraints(minWidth: 112.0),
+          padding: const EdgeDims.all(16.0),
+          child: new Flex(children)
+        )]
+      )
     );
   }
 }