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

Source/core/imagebitmap/ImageBitmapFactories.h

 /*
  * Copyright (c) 2013, 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 73 matching lines @@
     class ImageBitmapLoader FINAL : public GarbageCollectedFinalized<ImageBitmapLoader>, public FileReaderLoaderClient {
     public:
         static ImageBitmapLoader* create(ImageBitmapFactories& factory, const IntRect& cropRect, ScriptState* scriptState)
         {
             return new ImageBitmapLoader(factory, cropRect, scriptState);
         }
 
         void loadBlobAsync(ExecutionContext*, Blob*);
         ScriptPromise promise() { return m_resolver->promise(); }
 
-        void trace(Visitor*);
+        virtual void trace(Visitor*);
 
         virtual ~ImageBitmapLoader() { }
 
     private:
         ImageBitmapLoader(ImageBitmapFactories&, const IntRect&, ScriptState*);
 
         void rejectPromise();
 
         // FileReaderLoaderClient
         virtual void didStartLoading() OVERRIDE { }
@@ skipping 14 matching lines @@
 
     void addLoader(ImageBitmapLoader*);
     void didFinishLoading(ImageBitmapLoader*);
 
     PersistentHeapHashSetWillBeHeapHashSet<Member<ImageBitmapLoader> > m_pendingLoaders;
 };
 
 } // namespace blink
 
 #endif // ImageBitmapFactories_h