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

Source/modules/encryptedmedia/MediaKeys.h

 /*
  * Copyright (C) 2013 Apple 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 41 matching lines @@
 
     const String& keySystem() const { return m_keySystem; }
 
     ScriptPromise createSession(ScriptState*, const String& initDataType, ArrayBuffer* initData, const String& sessionType);
     ScriptPromise createSession(ScriptState*, const String& initDataType, ArrayBufferView* initData, const String& sessionType);
 
     static bool isTypeSupported(const String& keySystem, const String& contentType);
 
     blink::WebContentDecryptionModule* contentDecryptionModule();
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
     // ContextLifecycleObserver
     virtual void contextDestroyed() OVERRIDE;
 
 private:
     friend class MediaKeysInitializer;
     MediaKeys(ExecutionContext*, const String& keySystem, PassOwnPtr<blink::WebContentDecryptionModule>);
 
     ScriptPromise createSessionInternal(ScriptState*, const String& initDataType, PassRefPtr<ArrayBuffer> initData, const String& sessionType);
 
     const String m_keySystem;
     OwnPtr<blink::WebContentDecryptionModule> m_cdm;
 };
 
 }
 
 #endif // MediaKeys_h