Disallow adding ContextLifecycleObservers during iteration.

Source/core/page/PageLifecycleObserver.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 26 matching lines @@
 class PageLifecycleNotifier;
 
 class CORE_EXPORT PageLifecycleObserver : public LifecycleObserver<Page, PageLifecycleObserver, PageLifecycleNotifier> {
 public:
     virtual void pageVisibilityChanged() { }
     virtual void didCommitLoad(LocalFrame*) { }
 
     Page* page() const { return lifecycleContext(); }
 
 protected:
-    explicit PageLifecycleObserver(Page*);
+    explicit PageLifecycleObserver(Page* page)
+        : LifecycleObserver(page)
+    {
+    }
+
 };
 
 } // namespace blink
 
 #endif // PageLifecycleObserver_h