Allow lazy removal of (context) lifecycle observers while stopping.

third_party/WebKit/Source/core/dom/ContextLifecycleNotifier.cpp

 /*
  * 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 46 matching lines @@
 #if DCHECK_IS_ON()
         DCHECK_EQ(activeDOMObject->getExecutionContext(), context());
         DCHECK(activeDOMObject->suspendIfNeededCalled());
 #endif
         activeDOMObject->suspend();
     }
 }
 
 void ContextLifecycleNotifier::notifyStoppingActiveDOMObjects()
 {
-    // Neither additions nor removals are allowed while iterating.
-    TemporaryChange<IterationState> scope(m_iterationState, AllowingNone);
-    for (ContextLifecycleObserver* observer : m_observers) {
+    // Observers may be removed, but handled after iteration has completed.
+    TemporaryChange<IterationState> scope(m_iterationState, AllowPendingRemoval);
+    ObserverSet observers;
+    m_observers.swap(observers);
+    for (ContextLifecycleObserver* observer : observers) {
         if (observer->observerType() != ContextLifecycleObserver::ActiveDOMObjectType)
             continue;
         ActiveDOMObject* activeDOMObject = static_cast<ActiveDOMObject*>(observer);
 #if DCHECK_IS_ON()
         DCHECK_EQ(activeDOMObject->getExecutionContext(), context());
         DCHECK(activeDOMObject->suspendIfNeededCalled());
 #endif
         activeDOMObject->stop();
     }
+    removePending(observers);
 }
 
 unsigned ContextLifecycleNotifier::activeDOMObjectCount() const
 {
+    DCHECK(!isIteratingOverObservers());
     unsigned activeDOMObjects = 0;
     for (ContextLifecycleObserver* observer : m_observers) {
         if (observer->observerType() != ContextLifecycleObserver::ActiveDOMObjectType)
             continue;
         activeDOMObjects++;
     }
     return activeDOMObjects;
 }
 
 #if DCHECK_IS_ON()
 bool ContextLifecycleNotifier::contains(ActiveDOMObject* object) const
 {
+    DCHECK(!isIteratingOverObservers());
     for (ContextLifecycleObserver* observer : m_observers) {
         if (observer->observerType() != ContextLifecycleObserver::ActiveDOMObjectType)
             continue;
         ActiveDOMObject* activeDOMObject = static_cast<ActiveDOMObject*>(observer);
         if (activeDOMObject == object)
             return true;
     }
     return false;
 }
 #endif
 
 } // namespace blink