Have StyleResolverParentPusher / SelectorFilter deal with references

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index 51d87a6e34177017176ee62c432aa0b6ac3feb78..e66b7c64372e803ffc1f6c7be363f2db50ead9a0 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -183,8 +183,8 @@ public:
     // These should move to some global tree-walk state, or should be contained in a
     // TreeWalkContext or similar which is passed in to StyleResolver methods when available.
     // Using these during tree walk will allow style selector to optimize child and descendant selector lookups.
-    void pushParentElement(Element*);
-    void popParentElement(Element*);
+    void pushParentElement(Element&);
+    void popParentElement(Element&);
     void pushParentShadowRoot(const ShadowRoot&);
     void popParentShadowRoot(const ShadowRoot&);