StyleResolver should update RuleSets lazily.

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 375 matching lines @@
     bool isSrcdocDocument() const { return m_isSrcdocDocument; }
     bool isMobileDocument() const { return m_isMobileDocument; }
 
     StyleResolver* styleResolverIfExists() const { return m_styleResolver.get(); }
 
     bool isViewSource() const { return m_isViewSource; }
     void setIsViewSource(bool);
 
     bool sawElementsInKnownNamespaces() const { return m_sawElementsInKnownNamespaces; }
 
-    StyleResolver* styleResolver()
-    {
-        if (!m_styleResolver)
-            createStyleResolver();
-        return m_styleResolver.get();
-    }
+    StyleResolver* styleResolver();
 
     void notifyRemovePendingSheetIfNeeded();
 
     bool haveStylesheetsLoaded() const;
     bool haveStylesheetsAndImportsLoaded() const { return haveImportsLoaded() && haveStylesheetsLoaded(); }
 
     // This is a DOM function.
     StyleSheetList* styleSheets();
 
     StyleEngine* styleEngine() { return m_styleEngine.get(); }
@@ skipping 964 matching lines @@
 inline bool Node::isDocumentNode() const
 {
     return this == documentInternal();
 }
 
 Node* eventTargetNodeForDocument(Document*);
 
 } // namespace WebCore
 
 #endif // Document_h