LifecycleObserver::contextDestroyed should be explicitly dispatched promptly when a context is dest…

Source/platform/LifecycleNotifier.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * 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 27 matching lines @@
 class LifecycleNotifier {
 public:
     typedef LifecycleObserver<T> Observer;
     typedef T Context;
 
     static PassOwnPtr<LifecycleNotifier> create(Context* context)
     {
         return adoptPtr(new LifecycleNotifier(context));
     }
 
+    virtual ~LifecycleNotifier()
+    {
+        ASSERT(!m_observers.size());
+        ASSERT(!m_context);
+    }
 
-    virtual ~LifecycleNotifier();
-
+    void contextDestroyed();
 
     // FIXME: this won't need to be virtual anymore.
     virtual void addObserver(Observer*);
     virtual void removeObserver(Observer*);
 
     bool isIteratingOverObservers() const { return m_iterating != IteratingNone; }
 
 protected:
     explicit LifecycleNotifier(Context* context)
         : m_iterating(IteratingNone)
@@ skipping 16 matching lines @@
     IterationType m_iterating;
 
 private:
     typedef HashSet<Observer*> ObserverSet;
 
     ObserverSet m_observers;
     Context* m_context;
 };
 
 template<typename T>
-inline LifecycleNotifier<T>::~LifecycleNotifier()
+inline void LifecycleNotifier<T>::contextDestroyed()
 {
     TemporaryChange<IterationType> scope(this->m_iterating, IteratingOverAll);
     for (typename ObserverSet::iterator it = m_observers.begin(); it != m_observers.end(); it = m_observers.begin()) {
         Observer* observer = *it;
         m_observers.remove(observer);
         ASSERT(observer->lifecycleContext() == m_context);
         observer->contextDestroyed();
     }
+    m_context = nullptr;
 }
 
 template<typename T>
 inline void LifecycleNotifier<T>::addObserver(typename LifecycleNotifier<T>::Observer* observer)
 {
     RELEASE_ASSERT(m_iterating != IteratingOverAll);
     m_observers.add(observer);
 }
 
 template<typename T>
 inline void LifecycleNotifier<T>::removeObserver(typename LifecycleNotifier<T>::Observer* observer)
 {
     RELEASE_ASSERT(m_iterating != IteratingOverAll);
     m_observers.remove(observer);
 }
 
 
 
 } // namespace blink
 
 #endif // LifecycleNotifier_h