Don't assert when we do a rule tree GC and the root nodes still has s…

…trong references.

It could still have children.

components/style/rule_tree/mod.rs

@@ -440,8 +440,7 @@ impl StrongRuleNode {
         // script.
         debug_assert!(!thread_state::get().is_worker() &&
                       (thread_state::get().is_layout() ||
-                       (thread_state::get().is_script() &&
-                        me.refcount.load(Ordering::SeqCst) == 0)));
+                       thread_state::get().is_script()));
         let current = me.next_free.load(Ordering::SeqCst);
 
         if current == FREE_LIST_SENTINEL {