Bug 1883796 - Deal with an assert that doesn't hold always. r=dshin

During an animation restyle, two links might share the same rules while
not sharing the same link-ness.

This is a temporary state, but let's deal with it correctly.

Differential Revision: https://phabricator.services.mozilla.com/D203891

servo/components/style/sharing/mod.rs

@@ -908,12 +908,7 @@ impl<E: TElement> StyleSharingCache<E> {
             // RELEVANT_LINK_VISITED flag, so we can't share by rule node between visited and
             // unvisited styles. We don't check for visitedness and just refuse to share for links
             // entirely, so that visitedness doesn't affect timing.
-            debug_assert_eq!(
-                target.is_link(),
-                candidate.element.is_link(),
-                "Linkness mismatch"
-            );
-            if target.is_link() {
+            if target.is_link() || candidate.element.is_link() {
                 return None;
             }
 

testing/web-platform/tests/css/selectors/link-sharing-crash.html

@@ -0,0 +1,11 @@
+<link rel="help" href="https://bugzil.la/1883796">
+<script>
+window.addEventListener("load", () => {
+  let a = document.createElementNS("http://www.w3.org/1999/xhtml", "a")
+  document.documentElement.appendChild(a)
+  document.documentElement.appendChild(document.createElementNS("http://www.w3.org/1999/xhtml", "a"))
+  document.documentElement.scrollTo(-1132, 16)
+  document.documentElement.animate({"webkitTextStrokeWidth": ["197792984.89ex", "thin"]}, 2814)
+  a.setAttribute("href", "x")
+})
+</script>