servo: Merge #19453 - style: Add a fast-path for GeckoElement::is_root (from emilio:is-root-is-slow); r=upsuper

Source-Repo: https://github.com/servo/servo
Source-Revision: bca8951182dc3608f3d8c6948bcce636f7860529

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : da8b2d4567782e69c382bc63f3d050720e62353c

servo/components/style/gecko/wrapper.rs

@@ -1917,6 +1917,15 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
 
     #[inline]
     fn is_root(&self) -> bool {
+        let parent_node = match self.as_node().parent_node() {
+            Some(parent_node) => parent_node,
+            None => return false,
+        };
+
+        if !parent_node.is_document() {
+            return false;
+        }
+
         unsafe {
             Gecko_IsRootElement(self.0)
         }