Have Node::document() return a reference instead of a pointer

Source/core/xml/XPathStep.cpp

Index: Source/core/xml/XPathStep.cpp
diff --git a/Source/core/xml/XPathStep.cpp b/Source/core/xml/XPathStep.cpp
index dee7834c803d9e55edeb0efda07646c013b2df93..618a4216c7b3d55fe56d11469e3899174aee87e3 100644
--- a/Source/core/xml/XPathStep.cpp
+++ b/Source/core/xml/XPathStep.cpp
@@ -192,7 +192,7 @@ static inline bool nodeMatchesBasicTest(Node* node, Step::Axis axis, const Step:
             if (name == starAtom)
                 return namespaceURI.isEmpty() || namespaceURI == node->namespaceURI();
 
-            if (node->document()->isHTMLDocument()) {
+            if (node->document().isHTMLDocument()) {
                 if (node->isHTMLElement()) {
                     // Paths without namespaces should match HTML elements in HTML documents despite those having an XHTML namespace. Names are compared case-insensitively.
                     return equalIgnoringCase(toElement(node)->localName(), name) && (namespaceURI.isNull() || namespaceURI == node->namespaceURI());