StyleSheetContents doesn't need a set of clients.

sky/engine/core/css/StyleSheetContents.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 25 matching lines @@
 namespace blink {
 
 class CSSStyleSheet;
 class Document;
 class Node;
 class StyleRuleBase;
 class StyleRuleFontFace;
 
 class StyleSheetContents : public RefCounted<StyleSheetContents> {
 public:
-    static PassRefPtr<StyleSheetContents> create(const CSSParserContext& context)
+    static PassRefPtr<StyleSheetContents> create(Document* document, const CSSParserContext& context)
     {
-        return adoptRef(new StyleSheetContents(context));
+        return adoptRef(new StyleSheetContents(document, context));
     }
 
     ~StyleSheetContents();
 
     const CSSParserContext& parserContext() const { return m_parserContext; }
 
     bool parseString(const String&);
 
     void parserAppendRule(PassRefPtr<StyleRuleBase>);
 
     const Vector<RefPtr<StyleRuleBase> >& childRules() const { return m_childRules; }
 
-    void registerClient(CSSStyleSheet*);
-    void unregisterClient(CSSStyleSheet*);
-
     void shrinkToFit();
     RuleSet& ruleSet() { ASSERT(m_ruleSet); return *m_ruleSet.get(); }
     RuleSet& ensureRuleSet(AddRuleFlags);
-    void clearRuleSet();
 
 private:
-    explicit StyleSheetContents(const CSSParserContext&);
+    explicit StyleSheetContents(Document* document, const CSSParserContext&);
 
     OwnPtr<RuleSet> m_ruleSet;
     Vector<RefPtr<StyleRuleBase> > m_childRules;
     CSSParserContext m_parserContext;
 
-    HashSet<RawPtr<CSSStyleSheet> > m_clients;
+    RefPtr<Document> m_document;
 };
 
 } // namespace
 
 #endif  // SKY_ENGINE_CORE_CSS_STYLESHEETCONTENTS_H_