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

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 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 484 matching lines @@
 public:
     static PassOwnPtrWillBeRawPtr<WebGLRenderingContextLostCallback> create(WebGLRenderingContextBase* context)
     {
         return adoptPtrWillBeNoop(new WebGLRenderingContextLostCallback(context));
     }
 
     virtual ~WebGLRenderingContextLostCallback() { }
 
     virtual void onContextLost() { m_context->forceLostContext(WebGLRenderingContextBase::RealLostContext); }
 
-    void trace(Visitor* visitor)
+    virtual void trace(Visitor* visitor)
     {
         visitor->trace(m_context);
     }
 
 private:
     explicit WebGLRenderingContextLostCallback(WebGLRenderingContextBase* context)
         : m_context(context) { }
 
     RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
 };
 
 class WebGLRenderingContextErrorMessageCallback FINAL : public NoBaseWillBeGarbageCollectedFinalized<WebGLRenderingContextErrorMessageCallback>, public blink::WebGraphicsContext3D::WebGraphicsErrorMessageCallback {
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
 public:
     static PassOwnPtrWillBeRawPtr<WebGLRenderingContextErrorMessageCallback> create(WebGLRenderingContextBase* context)
     {
         return adoptPtrWillBeNoop(new WebGLRenderingContextErrorMessageCallback(context));
     }
 
     virtual ~WebGLRenderingContextErrorMessageCallback() { }
 
     virtual void onErrorMessage(const blink::WebString& message, blink::WGC3Dint)
     {
         if (m_context->m_synthesizedErrorsToConsole)
             m_context->printGLErrorToConsole(message);
         InspectorInstrumentation::didFireWebGLErrorOrWarning(m_context->canvas(), message);
     }
 
-    void trace(Visitor* visitor)
+    virtual void trace(Visitor* visitor)
     {
         visitor->trace(m_context);
     }
 
 private:
     explicit WebGLRenderingContextErrorMessageCallback(WebGLRenderingContextBase* context)
         : m_context(context) { }
 
     RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
 };
@@ skipping 5212 matching lines @@
     return m_sharedWebGraphicsContext3D ? m_sharedWebGraphicsContext3D->drawingBuffer() : 0;
 }
 #else
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 #endif
 
 } // namespace blink