servo: Merge #19367 - style: Make a Servo-only assertion apply to Gecko too (from emilio:gecko-assert); r=upsuper

Gecko passes it now, and we want to know if that ever changes.

Source-Repo: https://github.com/servo/servo
Source-Revision: 8349be1b3e768b85fbb09ecb3dd4e9480a24f29e

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 2582aced86ba89e34fe59bef17af04c8fdb587a6

servo/components/style/traversal.rs

@@ -256,8 +256,10 @@ pub trait DomTraversal<E: TElement> : Sync {
         parent: E,
         parent_data: &ElementData,
     ) -> bool {
-        debug_assert!(cfg!(feature = "gecko") ||
-                      parent.has_current_styles_for_traversal(parent_data, context.shared.traversal_flags));
+        debug_assert!(parent.has_current_styles_for_traversal(
+            parent_data,
+            context.shared.traversal_flags,
+        ));
 
         // If the parent computed display:none, we don't style the subtree.
         if parent_data.styles.is_display_none() {