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

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 759 matching lines @@
     if (!typeExtension.isEmpty())
         CustomElementRegistrationContext::setIsAttributeAndTypeExtension(element.get(), typeExtension);
 
     return element.release();
 }
 
 static inline QualifiedName createQualifiedName(const AtomicString& namespaceURI, const AtomicString& qualifiedName, ExceptionState& exceptionState)
 {
     AtomicString prefix, localName;
     if (!Document::parseQualifiedName(qualifiedName, prefix, localName, exceptionState))
-        return nullQName();
+        return QualifiedName::null();
 
     QualifiedName qName(prefix, localName, namespaceURI);
     if (!Document::hasValidNamespaceForElements(qName)) {
         exceptionState.throwDOMException(NamespaceError, "The namespace URI provided ('" + namespaceURI + "') is not valid for the qualified name provided ('" + qualifiedName + "').");
-        return nullQName();
+        return QualifiedName::null();
     }
 
     return qName;
 }
 
 PassRefPtrWillBeRawPtr<Element> Document::createElementNS(const AtomicString& namespaceURI, const AtomicString& qualifiedName, ExceptionState& exceptionState)
 {
     QualifiedName qName(createQualifiedName(namespaceURI, qualifiedName, exceptionState));
-    if (qName == nullQName())
+    if (qName == QualifiedName::null())
         return nullptr;
 
     return createElement(qName, false);
 }
 
 PassRefPtrWillBeRawPtr<Element> Document::createElementNS(const AtomicString& namespaceURI, const AtomicString& qualifiedName, const AtomicString& typeExtension, ExceptionState& exceptionState)
 {
     QualifiedName qName(createQualifiedName(namespaceURI, qualifiedName, exceptionState));
-    if (qName == nullQName())
+    if (qName == QualifiedName::null())
         return nullptr;
 
     RefPtrWillBeRawPtr<Element> element;
     if (CustomElement::isValidName(qName.localName()) && registrationContext())
         element = registrationContext()->createCustomTagElement(*this, qName);
     else
         element = createElement(qName, false);
 
     if (!typeExtension.isEmpty())
         CustomElementRegistrationContext::setIsAttributeAndTypeExtension(element.get(), typeExtension);
@@ skipping 5019 matching lines @@
     visitor->trace(m_compositorPendingAnimations);
     visitor->trace(m_contextDocument);
     visitor->registerWeakMembers<Document, &Document::clearWeakMembers>(this);
     DocumentSupplementable::trace(visitor);
     TreeScope::trace(visitor);
     ContainerNode::trace(visitor);
     ExecutionContext::trace(visitor);
 }
 
 } // namespace WebCore