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

Source/core/svg/SVGTransformListTearOff.cpp

 /*
  * 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 19 matching lines @@
 
 #include "config.h"
 #include "core/svg/SVGTransformListTearOff.h"
 
 #include "bindings/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/svg/SVGSVGElement.h"
 
 namespace WebCore {
 
-SVGTransformListTearOff::SVGTransformListTearOff(PassRefPtr<SVGTransformList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+SVGTransformListTearOff::SVGTransformListTearOff(PassRefPtr<SVGTransformList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
     : SVGListPropertyTearOffHelper<SVGTransformListTearOff, SVGTransformList>(target, contextElement, propertyIsAnimVal, attributeName)
 {
     ScriptWrappable::init(this);
 }
 
 SVGTransformListTearOff::~SVGTransformListTearOff()
 {
 }
 
 PassRefPtr<SVGTransformTearOff> SVGTransformListTearOff::createSVGTransformFromMatrix(PassRefPtr<SVGMatrixTearOff> matrix) const
 {
     return SVGSVGElement::createSVGTransformFromMatrix(matrix);
 }
 
 PassRefPtr<SVGTransformTearOff> SVGTransformListTearOff::consolidate(ExceptionState& exceptionState)
 {
     if (isImmutable()) {
         exceptionState.throwDOMException(NoModificationAllowedError, "The attribute is read-only.");
         return nullptr;
     }
 
     return createItemTearOff(target()->consolidate());
 }
 
 }