Have ElementTraversal / NodeTraversal's next() methods take a reference

Source/core/xml/XPathUtil.cpp

Index: Source/core/xml/XPathUtil.cpp
diff --git a/Source/core/xml/XPathUtil.cpp b/Source/core/xml/XPathUtil.cpp
index 5967efa025deb6385924c7dfb0fbff162d8ac9bd..5e266fa222d502a75345ebc508b90d9bc7ea572f 100644
--- a/Source/core/xml/XPathUtil.cpp
+++ b/Source/core/xml/XPathUtil.cpp
@@ -54,7 +54,7 @@ String stringValue(Node* node)
                 StringBuilder result;
                 result.reserveCapacity(1024);
 
-                for (Node* n = node->firstChild(); n; n = NodeTraversal::next(n, node)) {
+                for (Node* n = node->firstChild(); n; n = NodeTraversal::next(*n, node)) {
                     if (n->isTextNode()) {
                         const String& nodeValue = n->nodeValue();
                         result.append(nodeValue);