StyleResolver should update RuleSets lazily.

Source/core/dom/StyleEngine.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 10 matching lines @@
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #ifndef StyleEngine_h
 #define StyleEngine_h
 
+#include "core/css/resolver/StyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/DocumentOrderedList.h"
 #include "core/dom/DocumentStyleSheetCollection.h"
 #include "wtf/FastAllocBase.h"
 #include "wtf/ListHashSet.h"
 #include "wtf/RefPtr.h"
 #include "wtf/TemporaryChange.h"
 #include "wtf/Vector.h"
 #include "wtf/text/WTFString.h"
 
@@ skipping 92 matching lines @@
     void appendActiveAuthorStyleSheets(StyleResolver*);
     void getActiveAuthorStyleSheets(Vector<const Vector<RefPtr<CSSStyleSheet> >*>& activeAuthorStyleSheets) const;
 
     StyleResolver* resolverIfExists() const
     {
         return m_resolver.get();
     }
 
     StyleResolver* resolver()
     {
-        if (!m_resolver)
+        if (!m_resolver) {
             createResolver();
+        } else if (m_resolver->hasPendingAuthorStyleSheets()) {
+            m_resolver->appendPendingAuthorStyleSheets();
+        }
         return m_resolver.get();
     }
 
     bool hasResolver() const { return m_resolver.get(); }
     void clearResolver();
 
     CSSFontSelector* fontSelector();
     void didAttach();
     void didDetach();
     bool shouldClearResolver() const;
@@ skipping 49 matching lines @@
     bool m_ignorePendingStylesheets;
     bool m_didCalculateResolver;
     unsigned m_lastResolverAccessCount;
     Timer<StyleEngine> m_resolverThrowawayTimer;
     OwnPtr<StyleResolver> m_resolver;
 };
 
 }
 
 #endif