Oilpan: Trace DocumentVisibilityObserver::m_document.

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 361 matching lines @@
     {
         Document* document = toDocument(context);
         if (RefPtrWillBeRawPtr<Element> element = document->autofocusElement()) {
             document->setAutofocusElement(0);
             element->focus();
         }
     }
 };
 
 DocumentVisibilityObserver::DocumentVisibilityObserver(Document& document)
-    : m_document(0)
+    : m_document(nullptr)
 {
     registerObserver(document);
 }
 
 DocumentVisibilityObserver::~DocumentVisibilityObserver()
 {
 #if !ENABLE(OILPAN)
     unregisterObserver();
 #endif
 }
 
+void DocumentVisibilityObserver::trace(Visitor* visitor)
+{
+    visitor->trace(m_document);
+}
+
 void DocumentVisibilityObserver::unregisterObserver()
 {
     if (m_document) {
         m_document->unregisterVisibilityObserver(this);
-        m_document = 0;
+        m_document = nullptr;
     }
 }
 
 void DocumentVisibilityObserver::registerObserver(Document& document)
 {
     ASSERT(!m_document);
     m_document = &document;
     if (m_document)
         m_document->registerVisibilityObserver(this);
 }
@@ skipping 5439 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