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

Source/platform/network/SocketStreamHandleInternal.h

 /*
  * Copyright (C) 2012 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 52 matching lines @@
     virtual void didClose(blink::WebSocketStreamHandle*);
     virtual void didFail(blink::WebSocketStreamHandle*, const blink::WebSocketStreamError&);
 
     static blink::WebSocketStreamHandle* toWebSocketStreamHandle(SocketStreamHandle* handle)
     {
         if (handle && handle->m_internal)
             return handle->m_internal->m_socket.get();
         return 0;
     }
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
 private:
     explicit SocketStreamHandleInternal(SocketStreamHandle*);
 
     Member<SocketStreamHandle> m_handle;
     OwnPtr<blink::WebSocketStreamHandle> m_socket;
     int m_maxPendingSendAllowed;
     int m_pendingAmountSent;
 };
 
 } // namespace blink
 
 #endif // SocketStreamHandleInternal_h