Simplify contextDestroyed() notifications.

third_party/WebKit/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 40 matching lines @@
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         visitor->trace(m_observers);
     }
 
     bool isIteratingOverObservers() const { return m_iterating != IteratingNone; }
 
 protected:
     LifecycleNotifier()
         : m_iterating(IteratingNone)
-        , m_didCallContextDestroyed(false)
     {
     }
 
     enum IterationType {
         IteratingNone,
         IteratingOverAll,
     };
 
     IterationType m_iterating;
 
 protected:
     using ObserverSet = HeapHashSet<WeakMember<Observer>>;
 
     ObserverSet m_observers;
 
 #if DCHECK_IS_ON()
     T* context() { return static_cast<T*>(this); }
 #endif
-
-private:
-    bool m_didCallContextDestroyed;
 };
 
 template<typename T, typename Observer>
 inline LifecycleNotifier<T, Observer>::~LifecycleNotifier()
 {
     // FIXME: Enable the following ASSERT. Also see a FIXME in Document::detach().
-    // ASSERT(!m_observers.size() || m_didCallContextDestroyed);
+    // ASSERT(!m_observers.size());
 }
 
 template<typename T, typename Observer>
 inline void LifecycleNotifier<T, Observer>::notifyContextDestroyed()
 {
-    // Don't notify contextDestroyed() twice.
-    if (m_didCallContextDestroyed)
-        return;
-
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
-    Vector<UntracedMember<Observer>> snapshotOfObservers;
-    copyToVector(m_observers, snapshotOfObservers);
-    for (Observer* observer : snapshotOfObservers) {
-        if (!m_observers.contains(observer))
-            continue;
-
+    ObserverSet observers;
+    m_observers.swap(observers);
+    for (Observer* observer : observers) {
         ASSERT(observer->lifecycleContext() == context());
         observer->contextDestroyed();
     }
-
-    m_didCallContextDestroyed = true;
 }
 
 template<typename T, typename Observer>
 inline void LifecycleNotifier<T, Observer>::addObserver(Observer* observer)
 {
     RELEASE_ASSERT(m_iterating != IteratingOverAll);
     m_observers.add(observer);
 }
 
 template<typename T, typename Observer>
 inline void LifecycleNotifier<T, Observer>::removeObserver(Observer* observer)
 {
     m_observers.remove(observer);
 }
 
 } // namespace blink
 
 #endif // LifecycleNotifier_h