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

Source/core/svg/SVGPathSegListTearOff.h

Index: Source/core/svg/SVGPathSegListTearOff.h
diff --git a/Source/core/svg/SVGPathSegListTearOff.h b/Source/core/svg/SVGPathSegListTearOff.h
index f360f34fca57a23e7a83fd95d0238573f0afad1c..08da12eeb7fd6cf040da5bc4061b7822ea8193ee 100644
--- a/Source/core/svg/SVGPathSegListTearOff.h
+++ b/Source/core/svg/SVGPathSegListTearOff.h
@@ -60,13 +60,13 @@ class SVGPathSegListTearOff FINAL :
     public SVGListPropertyTearOffHelper<SVGPathSegListTearOff, SVGPathSegList>,
     public ScriptWrappable {
 public:
-    static PassRefPtr<SVGPathSegListTearOff> create(PassRefPtr<SVGPathSegList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    static PassRefPtr<SVGPathSegListTearOff> create(PassRefPtr<SVGPathSegList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
     {
         return adoptRef(new SVGPathSegListTearOff(target, contextElement, propertyIsAnimVal, attributeName));
     }
 
 private:
-    SVGPathSegListTearOff(PassRefPtr<SVGPathSegList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = nullQName())
+    SVGPathSegListTearOff(PassRefPtr<SVGPathSegList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
         : SVGListPropertyTearOffHelper<SVGPathSegListTearOff, SVGPathSegList>(target, contextElement, propertyIsAnimVal, attributeName)
     {
         ScriptWrappable::init(this);