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

Source/core/svg/SVGAngleTearOff.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 21 matching lines @@
 #define SVGAngleTearOff_h
 
 #include "bindings/v8/ScriptWrappable.h"
 #include "core/svg/SVGAngle.h"
 #include "core/svg/properties/SVGPropertyTearOff.h"
 
 namespace WebCore {
 
 class SVGAngleTearOff FINAL : public SVGPropertyTearOff<SVGAngle>, public ScriptWrappable {
 public:
-    static PassRefPtr<SVGAngleTearOff> create(PassRefPtr<SVGAngle> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    static PassRefPtr<SVGAngleTearOff> create(PassRefPtr<SVGAngle> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
     {
         return adoptRef(new SVGAngleTearOff(target, contextElement, propertyIsAnimVal, attributeName));
     }
 
     enum {
         SVG_ANGLETYPE_UNKNOWN = SVGAngle::SVG_ANGLETYPE_UNKNOWN,
         SVG_ANGLETYPE_UNSPECIFIED = SVGAngle::SVG_ANGLETYPE_UNSPECIFIED,
         SVG_ANGLETYPE_DEG = SVGAngle::SVG_ANGLETYPE_DEG,
         SVG_ANGLETYPE_RAD = SVGAngle::SVG_ANGLETYPE_RAD,
         SVG_ANGLETYPE_GRAD = SVGAngle::SVG_ANGLETYPE_GRAD
@@ skipping 15 matching lines @@
     String valueAsString() { return target()->valueAsString(); }
     void setValueAsString(const String&, ExceptionState&);
 
 private:
     SVGAngleTearOff(PassRefPtr<SVGAngle>, SVGElement*, PropertyIsAnimValType, const QualifiedName&);
 };
 
 } // namespace WebCore
 
 #endif // SVGAngleTearOff_h_