Do not consider title from non-css stylesheet for preferred set.

Source/core/dom/DocumentStyleSheetCollection.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 301 matching lines @@
                 sheet = static_cast<SVGStyleElement*>(n)->sheet();
             else if (e->hasLocalName(linkTag))
                 sheet = static_cast<HTMLLinkElement*>(n)->sheet();
             else
                 // <STYLE> element
                 sheet = static_cast<HTMLStyleElement*>(n)->sheet();
             // Check to see if this sheet belongs to a styleset
             // (thus making it PREFERRED or ALTERNATE rather than
             // PERSISTENT).
             AtomicString rel = e->getAttribute(relAttr);
-            if (!enabledViaScript && !title.isEmpty()) {
+            if (!enabledViaScript && sheet && !title.isEmpty()) {
                 // Yes, we have a title.
                 if (m_preferredStylesheetSetName.isEmpty()) {
                     // No preferred set has been established. If
                     // we are NOT an alternate sheet, then establish
                     // us as the preferred set. Otherwise, just ignore
                     // this sheet.
                     if (e->hasLocalName(styleTag) || !rel.contains("alternate"))
                         m_preferredStylesheetSetName = m_selectedStylesheetSetName = title;
                 }
                 if (title != m_preferredStylesheetSetName)
@@ skipping 157 matching lines @@
     info.addMember(m_authorStyleSheets, "authorStyleSheets");
     info.addMember(m_activeAuthorStyleSheets, "activeAuthorStyleSheets");
     info.addMember(m_styleSheetsForStyleSheetList, "styleSheetsForStyleSheetList");
     info.addMember(m_styleSheetCandidateNodes, "styleSheetCandidateNodes");
     info.addMember(m_preferredStylesheetSetName, "preferredStylesheetSetName");
     info.addMember(m_selectedStylesheetSetName, "selectedStylesheetSetName");
     info.addMember(m_document, "document");
 }
 
 }