StyleSheetContents doesn't need a set of clients.

sky/engine/core/css/CSSStyleSheet.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 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 34 matching lines @@
 
 PassRefPtr<CSSStyleSheet> CSSStyleSheet::create(PassRefPtr<StyleSheetContents> sheet, Node* ownerNode)
 {
     ASSERT(sheet);
     return adoptRef(new CSSStyleSheet(sheet, ownerNode));
 }
 
 PassRefPtr<CSSStyleSheet> CSSStyleSheet::create(Node* ownerNode, const KURL& baseURL)
 {
     CSSParserContext parserContext(ownerNode->document(), 0, baseURL);
-    RefPtr<StyleSheetContents> sheet = StyleSheetContents::create(parserContext);
+    RefPtr<StyleSheetContents> sheet = StyleSheetContents::create(&ownerNode->document(), parserContext);
     return adoptRef(new CSSStyleSheet(sheet.release(), ownerNode));
 }
 
 CSSStyleSheet::CSSStyleSheet(PassRefPtr<StyleSheetContents> contents, Node* ownerNode)
     : m_contents(contents)
     , m_ownerNode(ownerNode)
 {
     ASSERT(isAcceptableCSSStyleSheetParent(ownerNode));
-    m_contents->registerClient(this);
 }
 
 CSSStyleSheet::~CSSStyleSheet()
 {
-    m_contents->unregisterClient(this);
 }
 
 void CSSStyleSheet::setMediaQueries(PassRefPtr<MediaQuerySet> mediaQueries)
 {
     m_mediaQueries = mediaQueries;
 
     // Add warning message to inspector whenever dpi/dpcm values are used for "screen" media.
     reportMediaQueryWarningIfNeeded(ownerDocument(), m_mediaQueries.get());
 }
 
 void CSSStyleSheet::clearOwnerNode()
 {
     if (Document* owner = ownerDocument())
         owner->modifiedStyleSheet(this);
-    if (m_ownerNode)
-        m_contents->unregisterClient(this);
     m_ownerNode = nullptr;
 }
 
 Document* CSSStyleSheet::ownerDocument() const
 {
     return ownerNode() ? &ownerNode()->document() : 0;
 }
 
 } // namespace blink