Don't expose any AtomicRefCell directly from style traits

This lets us experiment with how we store this data on the DOM side.

components/style/invalidation/element/state_and_attributes.rs

@@ -90,7 +90,7 @@ pub fn invalidated_descendants<E>(element: E, child: E)
 where
     E: TElement,
 {
-    if child.get_data().is_none() {
+    if !child.has_data() {
         return;
     }