Have ElementTraversal::firstWithin() take a reference

Source/core/css/StyleInvalidationAnalysis.h

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 23 matching lines @@
 
 class Document;
 class Node;
 class StyleSheetContents;
 
 class StyleInvalidationAnalysis {
 public:
     StyleInvalidationAnalysis(const Vector<StyleSheetContents*>&);
 
     bool dirtiesAllStyle() const { return m_dirtiesAllStyle; }
-    void invalidateStyle(Document*);
+    void invalidateStyle(Document&);
 
 private:
 
     void analyzeStyleSheet(StyleSheetContents*);
 
     bool m_dirtiesAllStyle;
     HashSet<StringImpl*> m_idScopes;
     HashSet<StringImpl*> m_classScopes;
     Vector<Node*, 8> m_scopingNodes;
 };
 
 }
 
 #endif