style: Properly forward ElementWrapper::blocks_ancestor_combinators.

Not doing it is buggy. I think the only outcome of it is that we may
over-invalidate, so it's probably not a huge deal, but worth doing it.

components/style/invalidation/element/element_wrapper.rs

@@ -351,4 +351,8 @@ impl<'a, E> Element for ElementWrapper<'a, E>
         self.element.pseudo_element_originating_element()
             .map(|e| ElementWrapper::new(e, self.snapshot_map))
     }
+
+    fn blocks_ancestor_combinators(&self) -> bool {
+        self.element.blocks_ancestor_combinators()
+    }
 }