Add font support to PageSerializer

Source/core/css/CSSImportRule.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2006, 2008, 2012 Apple 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 35 matching lines @@
     CSSStyleSheet* styleSheet() const;
 
 private:
     CSSImportRule(StyleRuleImport*, CSSStyleSheet*);
 
     RefPtr<StyleRuleImport> m_importRule;
     mutable RefPtr<MediaList> m_mediaCSSOMWrapper;
     mutable RefPtr<CSSStyleSheet> m_styleSheetCSSOMWrapper;
 };
 
+inline CSSImportRule* toCSSImportRule(CSSRule* rule)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(rule->type() == CSSRule::IMPORT_RULE);
+    return static_cast<CSSImportRule*>(rule);
+}
+
 } // namespace WebCore
 
 #endif // CSSImportRule_h