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

Source/web/WebPageSerializer.cpp

 /*
  * Copyright (C) 2009 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 48 matching lines @@
 #include "wtf/text/StringConcatenate.h"
 
 using namespace WebCore;
 
 namespace {
 
 KURL getSubResourceURLFromElement(Element* element)
 {
     ASSERT(element);
     const QualifiedName& attributeName = element->subResourceAttributeName();
-    if (attributeName == nullQName())
+    if (attributeName == QualifiedName::null())
         return KURL();
 
     String value = element->getAttribute(attributeName);
     // Ignore javascript content.
     if (value.isEmpty() || value.stripWhiteSpace().startsWith("javascript:", false))
         return KURL();
 
     return element->document().completeURL(value);
 }
 
@@ skipping 183 matching lines @@
 
 WebString WebPageSerializer::generateBaseTagDeclaration(const WebString& baseTarget)
 {
     if (baseTarget.isEmpty())
         return String("<base href=\".\">");
     String baseString = "<base href=\".\" target=\"" + static_cast<const String&>(baseTarget) + "\">";
     return baseString;
 }
 
 } // namespace blink