Have Node::highestAncestor() return a reference

Source/core/dom/ContainerNode.h

Index: Source/core/dom/ContainerNode.h
diff --git a/Source/core/dom/ContainerNode.h b/Source/core/dom/ContainerNode.h
index 65f0e04c65ed3f8dc91b8eae8fbf62c9b84ec52a..9f22455fb6293c486c1b297c6cad5844423ccf22 100644
--- a/Source/core/dom/ContainerNode.h
+++ b/Source/core/dom/ContainerNode.h
@@ -243,13 +243,13 @@ inline Node* Node::lastChild() const
     return toContainerNode(this)->lastChild();
 }
 
-inline Node* Node::highestAncestor() const
+inline Node& Node::highestAncestor() const
 {
     Node* node = const_cast<Node*>(this);
     Node* highest = node;
     for (; node; node = node->parentNode())
         highest = node;
-    return highest;
+    return *highest;
 }
 
 inline Node* Node::parentElementOrShadowRoot() const