Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/modules/indexeddb/IDBVersionChangeEvent.h

 /*
  * Copyright (C) 2011 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
@@ skipping 30 matching lines @@
     static PassRefPtr<IDBVersionChangeEvent> create(PassRefPtr<IDBAny> oldVersion = IDBAny::createNull(), PassRefPtr<IDBAny> newVersion = IDBAny::createNull(), const AtomicString& eventType = AtomicString(), blink::WebIDBDataLoss = blink::WebIDBDataLossNone, const String& dataLossMessage = String());
     virtual ~IDBVersionChangeEvent();
 
     ScriptValue oldVersion(ExecutionContext*) const;
     ScriptValue newVersion(ExecutionContext*) const;
     const AtomicString& dataLoss() const;
     const String& dataLossMessage() const { return m_dataLossMessage; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     IDBVersionChangeEvent(PassRefPtr<IDBAny> oldVersion, PassRefPtr<IDBAny> newVersion, const AtomicString& eventType, blink::WebIDBDataLoss, const String& dataLoss);
 
     RefPtr<IDBAny> m_oldVersion;
     RefPtr<IDBAny> m_newVersion;
     bool m_dataLoss;
     String m_dataLossMessage;
 };
 
 } // namespace WebCore
 
 #endif // IDBVersionChangeEvent_h