bindings: Supports [SaveSameObject] extended attribute.

third_party/WebKit/Source/core/css/CSSImportRule.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2005, 2006, 2008, 2009, 2010, 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 54 matching lines @@
             result.append(mediaText);
         }
     }
     result.append(';');
 
     return result.toString();
 }
 
 CSSStyleSheet* CSSImportRule::styleSheet() const
 {
+    // TODO(yukishiino): CSSImportRule.styleSheet attribute is not nullable,
+    // thus this function must not return nullptr.
     if (!m_importRule->styleSheet())
         return nullptr;
 
     if (!m_styleSheetCSSOMWrapper)
         m_styleSheetCSSOMWrapper = CSSStyleSheet::create(m_importRule->styleSheet(), const_cast<CSSImportRule*>(this));
     return m_styleSheetCSSOMWrapper.get();
 }
 
 void CSSImportRule::reattach(StyleRuleBase*)
 {
     // FIXME: Implement when enabling caching for stylesheets with import rules.
     ASSERT_NOT_REACHED();
 }
 
 DEFINE_TRACE(CSSImportRule)
 {
     visitor->trace(m_importRule);
     visitor->trace(m_mediaCSSOMWrapper);
     visitor->trace(m_styleSheetCSSOMWrapper);
     CSSRule::trace(visitor);
 }
 
 } // namespace blink