Oilpan: fix build after r183426.

Source/modules/geofencing/GeofencingEvent.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GeofencingEvent_h
 #define GeofencingEvent_h
 
 #include "modules/EventModules.h"
 #include "modules/geofencing/GeofencingRegion.h"
 #include "platform/heap/Handle.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class GeofencingRegion;
 
 // FIXME: This should derive from ExtendableEvent.
-class GeofencingEvent FINAL : public Event {
+class GeofencingEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<GeofencingEvent> create()
     {
         return adoptRefWillBeNoop(new GeofencingEvent);
     }
+
     static PassRefPtrWillBeRawPtr<GeofencingEvent> create(const AtomicString& type, const String& id, GeofencingRegion* region)
     {
         return adoptRefWillBeNoop(new GeofencingEvent(type, id, region));
     }
 
     virtual ~GeofencingEvent();
+    virtual void trace(Visitor*) override;
 
     virtual const AtomicString& interfaceName() const override;
 
     String id() const { return m_id; }
 
     GeofencingRegion* region() const { return m_region; }
 
 private:
     GeofencingEvent();
     GeofencingEvent(const AtomicString& type, const String& id, GeofencingRegion*);
     String m_id;
     PersistentWillBeMember<GeofencingRegion> m_region;
 };
 
 } // namespace blink
 
 #endif // GeofencingEvent_h