Remove single client special cases for StyleSheetContents.

sky/engine/core/dom/StyleEngine.cpp

 /*
  * 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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 372 matching lines @@
     if (result.isNewEntry || !result.storedValue->value) {
         styleSheet = CSSStyleSheet::create(e, KURL());
         styleSheet->contents()->parseString(text);
         if (result.isNewEntry) {
             result.storedValue->value = styleSheet->contents();
             m_sheetToTextCache.add(styleSheet->contents(), textContent);
         }
     } else {
         StyleSheetContents* contents = result.storedValue->value;
         ASSERT(contents);
-        ASSERT(contents->singleOwnerDocument() == e->document());
         styleSheet = CSSStyleSheet::create(contents, e);
     }
 
     ASSERT(styleSheet);
     return styleSheet;
 }
 
 void StyleEngine::removeSheet(StyleSheetContents* contents)
 {
     HashMap<RawPtr<StyleSheetContents>, AtomicString>::iterator it = m_sheetToTextCache.find(contents);
@@ skipping 15 matching lines @@
 {
     if (!document().isActive())
         return;
 
     if (m_resolver)
         m_resolver->invalidateMatchedPropertiesCache();
     document().setNeedsStyleRecalc(SubtreeStyleChange);
 }
 
 }