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

Source/build/scripts/templates/MakeQualifiedNames.cpp.tmpl

 {% from "macros.tmpl" import license %}
 {{ license() }}
 
 #include "config.h"
 
 #ifdef SKIP_STATIC_CONSTRUCTORS_ON_GCC
 #define {{namespace|to_macro_style}}_NAMES_HIDE_GLOBALS 1
-#else
-#define QNAME_DEFAULT_CONSTRUCTOR 1
 #endif
 
 #include "{{namespace}}Names.h"
 
 #include "wtf/StaticConstructors.h"
 
 namespace WebCore {
 namespace {{namespace}}Names {
 
 using namespace WebCore;
@@ skipping 52 matching lines @@
     {% if use_namespace_for_attrs %}
     createQualifiedName((void*)&{{attr|symbol}}Attr, {{attr|symbol}}Impl, {{namespace_prefix}}NS);
     {% else %}
     createQualifiedName((void*)&{{attr|symbol}}Attr, {{attr|symbol}}Impl);
     {% endif %}
     {% endfor %}
 }
 
 } // {{namespace}}
 } // WebCore