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

Source/core/timing/PerformanceTiming.h

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 56 matching lines @@
     unsigned long long responseStart() const;
     unsigned long long responseEnd() const;
     unsigned long long domLoading() const;
     unsigned long long domInteractive() const;
     unsigned long long domContentLoadedEventStart() const;
     unsigned long long domContentLoadedEventEnd() const;
     unsigned long long domComplete() const;
     unsigned long long loadEventStart() const;
     unsigned long long loadEventEnd() const;
 
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) { }
 
 private:
     explicit PerformanceTiming(LocalFrame*);
 
     const DocumentTiming* documentTiming() const;
     DocumentLoader* documentLoader() const;
     DocumentLoadTiming* documentLoadTiming() const;
     ResourceLoadTiming* resourceLoadTiming() const;
 
     unsigned long long monotonicTimeToIntegerMilliseconds(double) const;
 };
 
 }
 
 #endif // !defined(PerformanceTiming_h)