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

Source/platform/Timer.h

 /*
  * Copyright (C) 2006 Apple Computer, 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 55 matching lines @@
 
     void augmentRepeatInterval(double delta) {
         setNextFireTime(m_nextFireTime + delta);
         m_repeatInterval += delta;
     }
 
     void didChangeAlignmentInterval();
 
     static void fireTimersInNestedEventLoop();
 
+    virtual void trace(Visitor*) { }
+
 private:
     virtual void fired() = 0;
 
     virtual double alignedFireTime(double fireTime) const { return fireTime; }
 
     void checkConsistency() const;
     void checkHeapIndex() const;
 
     void setNextFireTime(double);
 
@@ skipping 103 matching lines @@
     TimerFiredClass* m_object;
     TimerFiredFunction m_function;
 
     double m_delay;
     bool m_shouldRestartWhenTimerFires;
 };
 
 }
 
 #endif