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

Source/core/svg/SVGPointListTearOff.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 22 matching lines @@
 
 #include "core/svg/SVGPointList.h"
 #include "core/svg/properties/SVGListPropertyTearOffHelper.h"
 
 namespace WebCore {
 
 class SVGPointListTearOff FINAL :
     public SVGListPropertyTearOffHelper<SVGPointListTearOff, SVGPointList>,
     public ScriptWrappable {
 public:
-    static PassRefPtr<SVGPointListTearOff> create(PassRefPtr<SVGPointList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    static PassRefPtr<SVGPointListTearOff> create(PassRefPtr<SVGPointList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
     {
         return adoptRef(new SVGPointListTearOff(target, contextElement, propertyIsAnimVal, attributeName));
     }
 
 private:
-    SVGPointListTearOff(PassRefPtr<SVGPointList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    SVGPointListTearOff(PassRefPtr<SVGPointList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
         : SVGListPropertyTearOffHelper<SVGPointListTearOff, SVGPointList>(target, contextElement, propertyIsAnimVal, attributeName)
     {
         ScriptWrappable::init(this);
     }
 };
 
 } // namespace WebCore
 
 #endif // SVGPointListTearOff_h_