Oilpan: Move LifecycleNotifier's hierarchy to Oilpan's heap

Source/core/dom/DocumentLifecycleNotifier.cpp

 /*
  * Copyright (C) 2013 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 55 matching lines @@
 
 #if !ENABLE(OILPAN)
 void DocumentLifecycleNotifier::notifyDocumentWasDisposed()
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverDocumentObservers);
     for (DocumentLifecycleObserver* observer : m_documentObservers)
         observer->documentWasDisposed();
 }
 #endif
 
+void DocumentLifecycleNotifier::trace(Visitor* visitor)
+{
+    visitor->trace(m_documentObservers);
+    LifecycleNotifier<Document>::trace(visitor);
+}
+
 } // namespace blink