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

Source/core/storage/StorageArea.h

 /*
  * Copyright (C) 2009 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 55 matching lines @@
 
     bool canAccessStorage(LocalFrame*);
     size_t memoryBytesUsedByCache();
 
     static void dispatchLocalStorageEvent(const String& key, const String& oldValue, const String& newValue,
         SecurityOrigin*, const KURL& pageURL, blink::WebStorageArea* sourceAreaInstance, bool originatedInProcess);
     static void dispatchSessionStorageEvent(const String& key, const String& oldValue, const String& newValue,
         SecurityOrigin*, const KURL& pageURL, const blink::WebStorageNamespace&,
         blink::WebStorageArea* sourceAreaInstance, bool originatedInProcess);
 
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) { }
 
 private:
     static bool isEventSource(Storage*, blink::WebStorageArea* sourceAreaInstance);
 
     OwnPtr<blink::WebStorageArea> m_storageArea;
     StorageType m_storageType;
     bool m_canAccessStorageCachedResult;
     LocalFrame* m_canAccessStorageCachedFrame;
 };
 
 } // namespace blink
 
 #endif // StorageArea_h