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

Source/modules/websockets/NewWebSocketChannelImpl.cpp

 /*
  * 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 54 matching lines @@
     virtual ~BlobLoader() { }
 
     void cancel();
 
     // FileReaderLoaderClient functions.
     virtual void didStartLoading() OVERRIDE { }
     virtual void didReceiveData() OVERRIDE { }
     virtual void didFinishLoading() OVERRIDE;
     virtual void didFail(FileError::ErrorCode) OVERRIDE;
 
-    void trace(Visitor* visitor)
+    virtual void trace(Visitor* visitor)
     {
         visitor->trace(m_channel);
     }
 
 private:
     Member<NewWebSocketChannelImpl> m_channel;
     FileReaderLoader m_loader;
 };
 
 NewWebSocketChannelImpl::BlobLoader::BlobLoader(PassRefPtr<BlobDataHandle> blobDataHandle, NewWebSocketChannelImpl* channel)
@@ skipping 471 matching lines @@
 }
 
 void NewWebSocketChannelImpl::trace(Visitor* visitor)
 {
     visitor->trace(m_blobLoader);
     visitor->trace(m_client);
     WebSocketChannel::trace(visitor);
 }
 
 } // namespace blink