Have ElementTraversal::firstWithin() take a reference

Source/core/dom/shadow/ElementShadow.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 64 matching lines @@
 
 private:
     ElementShadow();
 
     void removeAllShadowRoots();
     bool resolveApplyAuthorStyles() const;
 
     void distribute();
     void clearDistribution();
 
-    void collectSelectFeatureSetFrom(ShadowRoot*);
+    void collectSelectFeatureSetFrom(ShadowRoot&);
     void distributeNodeChildrenTo(InsertionPoint*, ContainerNode*);
 
     bool needsSelectFeatureSet() const { return m_needsSelectFeatureSet; }
     void setNeedsSelectFeatureSet() { m_needsSelectFeatureSet = true; }
 
     typedef HashMap<const Node*, DestinationInsertionPoints> NodeToDestinationInsertionPoints;
     NodeToDestinationInsertionPoints m_nodeToInsertionPoints;
 
     SelectRuleFeatureSet m_selectFeatures;
     DoublyLinkedList<ShadowRoot> m_shadowRoots;
@@ skipping 32 matching lines @@
 inline void ElementShadow::distributeIfNeeded()
 {
     if (m_needsDistributionRecalc)
         distribute();
     m_needsDistributionRecalc = false;
 }
 
 } // namespace
 
 #endif