Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/core/xml/XMLHttpRequestProgressEventThrottle.h

 /*
  * Copyright (C) 2010 Julien Chaffraix <jchaffraix@webkit.org>
  * All right 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 48 matching lines @@
     // ProgressEvent overwrites the existing. I.e. only the latest one gets
     // queued. If the timer is running, this method just updates
     // m_lengthComputable, m_loaded and m_total. They'll be used on next
     // fired() call.
     void dispatchProgressEvent(const AtomicString&, bool lengthComputable, unsigned long long loaded, unsigned long long total);
     void dispatchReadyStateChangeEvent(PassRefPtrWillBeRawPtr<Event>, ProgressEventAction = DoNotFlushProgressEvent);
 
     void suspend();
     void resume();
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
 private:
     static const double minimumProgressEventDispatchingIntervalInSeconds;
 
     // Dispatches an event. If suspended, just queues the given event.
     void dispatchEvent(PassRefPtrWillBeRawPtr<Event>);
 
     virtual void fired() OVERRIDE;
     void dispatchDeferredEvents(Timer<XMLHttpRequestProgressEventThrottle>*);
     bool flushDeferredProgressEvent();
@@ skipping 13 matching lines @@
 
     bool m_deferEvents;
     RefPtrWillBeMember<Event> m_deferredProgressEvent;
     WillBeHeapVector<RefPtrWillBeMember<Event> > m_deferredEvents;
     Timer<XMLHttpRequestProgressEventThrottle> m_dispatchDeferredEventsTimer;
 };
 
 } // namespace blink
 
 #endif // XMLHttpRequestProgressEventThrottle_h