[Oilpan] Prepare full definition of classes before using Member

third_party/WebKit/Source/core/events/PopStateEvent.h

 /*
  * Copyright (C) 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 33 matching lines @@
     static PassRefPtrWillBeRawPtr<PopStateEvent> create(PassRefPtr<SerializedScriptValue>, History*);
     static PassRefPtrWillBeRawPtr<PopStateEvent> create(const AtomicString&, const PopStateEventInit&);
 
     ScriptValue state() const { return m_state; }
     SerializedScriptValue* serializedState() const { return m_serializedState.get(); }
     void setSerializedState(PassRefPtr<SerializedScriptValue> state)
     {
         ASSERT(!m_serializedState);
         m_serializedState = state;
     }
-    History* history() const { return m_history.get(); }
+    History* history() const;
 
     const AtomicString& interfaceName() const override;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     PopStateEvent();
     PopStateEvent(const AtomicString&, const PopStateEventInit&);
     PopStateEvent(PassRefPtr<SerializedScriptValue>, History*);
 
     RefPtr<SerializedScriptValue> m_serializedState;
     ScriptValue m_state;
     PersistentWillBeMember<History> m_history;
 };
 
 } // namespace blink
 
 #endif // PopStateEvent_h