Oilpan: have Storage objects reside on the heap by default.

Source/modules/storage/StorageEvent.h

 /*
  * Copyright (C) 2008, 2009 Apple 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 49 matching lines @@
 
 private:
     StorageEvent();
     StorageEvent(const AtomicString& type, const String& key, const String& oldValue, const String& newValue, const String& url, Storage* storageArea);
     StorageEvent(const AtomicString&, const StorageEventInit&);
 
     String m_key;
     String m_oldValue;
     String m_newValue;
     String m_url;
-    RefPtrWillBeMember<Storage> m_storageArea;
+    PersistentWillBeMember<Storage> m_storageArea;
 };
 
 } // namespace blink
 
 #endif // StorageEvent_h