[oilpan]: Avoid refcounting QualifiedName's nullQName when tracing.

Source/core/svg/SVGStringListTearOff.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 20 matching lines @@
 #ifndef SVGStringListTearOff_h
 #define SVGStringListTearOff_h
 
 #include "core/svg/SVGStringList.h"
 #include "core/svg/properties/SVGPropertyTearOff.h"
 
 namespace WebCore {
 
 class SVGStringListTearOff : public SVGPropertyTearOff<SVGStringList>, public ScriptWrappable {
 public:
-    static PassRefPtr<SVGStringListTearOff> create(PassRefPtr<SVGStringList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    static PassRefPtr<SVGStringListTearOff> create(PassRefPtr<SVGStringList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
     {
         return adoptRef(new SVGStringListTearOff(target, contextElement, propertyIsAnimVal, attributeName));
     }
 
     // SVGStringList DOM interface:
 
     // WebIDL requires "unsigned long" type instead of size_t.
     unsigned long length()
     {
         return target()->length();
@@ skipping 86 matching lines @@
         return item;
     }
 
 protected:
     SVGStringListTearOff(PassRefPtr<SVGStringList>, SVGElement*, PropertyIsAnimValType, const QualifiedName&);
 };
 
 } // namespace WebCore
 
 #endif // SVGStringListTearOff_h_