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

Source/platform/LifecycleContext.h

 
 /*
  * 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:
  * 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
@@ skipping 18 matching lines @@
 #define LifecycleContext_h
 
 #include "platform/LifecycleNotifier.h"
 #include "platform/LifecycleObserver.h"
 #include "wtf/HashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
+class Visitor;
+
 template <typename T>
 class LifecycleContext {
 public:
     typedef LifecycleNotifier<T> Notifier;
     typedef LifecycleObserver<T> Observer;
 
     LifecycleContext() { }
     virtual ~LifecycleContext() { }
 
     virtual bool isContextThread() const { return true; }
 
     // Called from the constructor of observers.
     void wasObservedBy(Observer*);
 
     // Called from the destructor of observers.
     void wasUnobservedBy(Observer*);
 
+    virtual void trace(Visitor*) { }
+
 protected:
     Notifier& lifecycleNotifier();
 
 private:
     PassOwnPtr<Notifier> createLifecycleNotifier();
 
     OwnPtr<Notifier> m_lifecycleNotifier;
 };
 
 template<typename T>
@@ skipping 20 matching lines @@
 
 template<typename T>
 inline PassOwnPtr<typename LifecycleContext<T>::Notifier> LifecycleContext<T>::createLifecycleNotifier()
 {
     return LifecycleContext<T>::Notifier::create(static_cast<T*>(this));
 }
 
 } // namespace blink
 
 #endif // LifecycleContext_h