Have ElementTraversal::firstWithin() take a reference

Source/core/dom/DocumentOrderedMap.cpp

Index: Source/core/dom/DocumentOrderedMap.cpp
diff --git a/Source/core/dom/DocumentOrderedMap.cpp b/Source/core/dom/DocumentOrderedMap.cpp
index eb155a8906a46fd560fd22e188626b2e2450f91e..494d266768f241b113a78fb0a0392cc89a72707b 100644
--- a/Source/core/dom/DocumentOrderedMap.cpp
+++ b/Source/core/dom/DocumentOrderedMap.cpp
@@ -122,7 +122,8 @@ inline Element* DocumentOrderedMap::get(StringImpl* key, const TreeScope* scope)
 
     if (m_duplicateCounts.contains(key)) {
         // We know there's at least one node that matches; iterate to find the first one.
-        for (element = ElementTraversal::firstWithin(scope->rootNode()); element; element = ElementTraversal::next(*element)) {
+        ASSERT(scope->rootNode());
+        for (element = ElementTraversal::firstWithin(*scope->rootNode()); element; element = ElementTraversal::next(*element)) {
             if (!keyMatches(key, element))
                 continue;
             m_duplicateCounts.remove(key);