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

Source/core/html/HTMLLabelElement.cpp

Index: Source/core/html/HTMLLabelElement.cpp
diff --git a/Source/core/html/HTMLLabelElement.cpp b/Source/core/html/HTMLLabelElement.cpp
index e5b985e961e371dfda91a56eec02096deef5de15..f4cf27f6ee4fe149c3e5f6d52e54bdc0d9f4f408 100644
--- a/Source/core/html/HTMLLabelElement.cpp
+++ b/Source/core/html/HTMLLabelElement.cpp
@@ -70,7 +70,7 @@ LabelableElement* HTMLLabelElement::control()
         // per http://dev.w3.org/html5/spec/Overview.html#the-label-element
         // the form element must be "labelable form-associated element".
         Element* element = this;
-        while ((element = ElementTraversal::next(element, this))) {
+        while ((element = ElementTraversal::next(*element, this))) {
             if (!supportsLabels(element))
                 continue;
             return toLabelableElement(element);