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

Source/core/page/PageLifecycleNotifier.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 52 matching lines @@
         pageObserver->pageVisibilityChanged();
 }
 
 void PageLifecycleNotifier::notifyDidCommitLoad(LocalFrame* frame)
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverPageObservers);
     for (PageLifecycleObserver* pageObserver : m_pageObservers)
         pageObserver->didCommitLoad(frame);
 }
 
+void PageLifecycleNotifier::trace(Visitor* visitor)
+{
+    visitor->trace(m_pageObservers);
+    LifecycleNotifier<Page>::trace(visitor);
+}
+
 } // namespace blink