servo: Merge #16613 - Clear animation-only dirty descendants bit on display:none descendants (from birtles:clear-animation-dirty-bit); r=hiikezoe

PR for [Gecko bug 1359658](https://bugzilla.mozilla.org/show_bug.cgi?id=1359658)

When an element has a display:none ancestor we don't traverse it during
restyle. However, at the end of restyling we expect the tree to be free
of dirty bits. We currently take special care to clear the regular
(non-animation) dirty bit on nodes in display:none subtrees in order to
preserve this invariant. This patch applies the same handling to the
animation-only dirty descendants bit.

---
- [X] `./mach build -d` just keeps crashing because mozjs calls sed.exe in a way that breaks it
- [X] `./mach test-tidy` does not report any errors
- [X] There are tests for these changes on the Gecko side

Source-Repo: https://github.com/servo/servo
Source-Revision: e5762cb6953b5e202e8733e39e8267c4b67a9622

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 1e2beadc2bad4ad0c6fe2233d748a4e402c51ffd

servo/components/style/traversal.rs

@@ -537,7 +537,10 @@ pub fn resolve_style<E, F, G, H>(context: &mut StyleContext<E>, element: E,
     if !in_doc || display_none_root.is_some() {
         let mut curr = element;
         loop {
-            unsafe { curr.unset_dirty_descendants(); }
+            unsafe {
+                curr.unset_dirty_descendants();
+                curr.unset_animation_only_dirty_descendants();
+            }
             if in_doc && curr == display_none_root.unwrap() {
                 break;
             }
@@ -789,5 +792,8 @@ pub fn clear_descendant_data<E: TElement, F: Fn(E)>(el: E, clear_data: &F) {
         }
     }
 
-    unsafe { el.unset_dirty_descendants(); }
+    unsafe {
+        el.unset_dirty_descendants();
+        el.unset_animation_only_dirty_descendants();
+    }
 }