Disallow adding ContextLifecycleObservers during iteration.

Source/core/dom/ContextLifecycleNotifier.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 23 matching lines @@
 
 namespace blink {
 
 class ActiveDOMObject;
 class ContextLifecycleObserver;
 class ExecutionContext;
 
 class CORE_EXPORT ContextLifecycleNotifier : public LifecycleNotifier<ExecutionContext, ContextLifecycleObserver> {
     WTF_MAKE_NONCOPYABLE(ContextLifecycleNotifier);
 public:
-    void addObserver(ContextLifecycleObserver*);
-
     void notifyResumingActiveDOMObjects();
     void notifySuspendingActiveDOMObjects();
     void notifyStoppingActiveDOMObjects();
 
     unsigned activeDOMObjectCount() const;
     bool hasPendingActivity() const;
 
 protected:
     // Need a default constructor to link core and modules separately.
     // If no default constructor, we will see an error: "constructor for
     // 'blink::ExecutionContext' must explicitly initialize the base class
     // 'blink::ContextLifecycleNotifier' which does not have a default
     // constructor ExecutionContext::ExecutionContext()".
     ContextLifecycleNotifier() { }
 
 #if ENABLE(ASSERT)
     bool contains(ActiveDOMObject*) const;
 #endif
 };
 
 } // namespace blink
 
 #endif // ContextLifecycleNotifier_h