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

Source/web/WebMediaPlayerClientImpl.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:
  *
  *     * 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 101 matching lines @@
         explicit AudioClientImpl(blink::AudioSourceProviderClient* client)
             : m_client(client)
         {
         }
 
         virtual ~AudioClientImpl() { }
 
         // WebAudioSourceProviderClient
         virtual void setFormat(size_t numberOfChannels, float sampleRate) OVERRIDE;
 
-        void trace(Visitor*);
+        virtual void trace(Visitor*);
 
     private:
         RawPtrWillBeMember<blink::AudioSourceProviderClient> m_client;
     };
 
     // AudioSourceProviderImpl wraps a WebAudioSourceProvider.
     // provideInput() calls into Chromium to get a rendered audio stream.
 
     class AudioSourceProviderImpl FINAL : public blink::AudioSourceProvider {
     public:
@@ skipping 17 matching lines @@
         Mutex provideInputLock;
     };
 
     AudioSourceProviderImpl m_audioSourceProvider;
 #endif
 };
 
 } // namespace blink
 
 #endif