StyleSheet.ownerNode should be null when it gets orphaned.

Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google 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
@@ skipping 388 matching lines @@
     }
     // Completing the sheet load may cause scripts to execute.
     RefPtr<Node> protector(m_owner);
 
     CSSParserContext parserContext(m_owner->document(), baseURL, charset);
 
     if (RefPtr<StyleSheetContents> restoredSheet = const_cast<CachedCSSStyleSheet*>(cachedStyleSheet)->restoreParsedStyleSheet(parserContext)) {
         ASSERT(restoredSheet->isCacheable());
         ASSERT(!restoredSheet->isLoading());
 
+        if (m_sheet)
+            clearSheet();
         m_sheet = CSSStyleSheet::create(restoredSheet, m_owner);
         m_sheet->setMediaQueries(MediaQuerySet::create(m_owner->media()));
         m_sheet->setTitle(m_owner->title());
 
         m_loading = false;
         sheetLoaded();
         notifyLoadedSheetAndAllCriticalSubresources(false);
         return;
     }
 
     RefPtr<StyleSheetContents> styleSheet = StyleSheetContents::create(href, parserContext);
 
+    if (m_sheet)
+        clearSheet();
     m_sheet = CSSStyleSheet::create(styleSheet, m_owner);
     m_sheet->setMediaQueries(MediaQuerySet::create(m_owner->media()));
     m_sheet->setTitle(m_owner->title());
 
     styleSheet->parseAuthorStyleSheet(cachedStyleSheet, m_owner->document()->securityOrigin());
 
     m_loading = false;
     styleSheet->notifyLoadedSheet(cachedStyleSheet);
     styleSheet->checkLoaded();
 
@@ skipping 182 matching lines @@
 void LinkStyle::ownerRemoved()
 {
     if (m_sheet)
         clearSheet();
 
     if (styleSheetIsLoading())
         removePendingSheet(RemovePendingSheetNotifyLater);
 }
 
 } // namespace WebCore