Simplify ContextLifecycleNotifier's handling of ActiveDOMObjects.

Source/core/frame/DOMWindowLifecycleNotifier.cpp

 /*
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 39 matching lines @@
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     for (DOMWindowLifecycleObserver* observer : m_observers)
         observer->didAddEventListener(window, eventType);
 }
 
 void DOMWindowLifecycleNotifier::notifyRemoveEventListener(LocalDOMWindow* window, const AtomicString& eventType)
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     for (DOMWindowLifecycleObserver* observer : m_observers)
-        static_cast<DOMWindowLifecycleObserver*>(observer)->didRemoveEventListener(window, eventType);
+        observer->didRemoveEventListener(window, eventType);
 }
 
 void DOMWindowLifecycleNotifier::notifyRemoveAllEventListeners(LocalDOMWindow* window)
 {
     TemporaryChange<IterationType> scope(m_iterating, IteratingOverAll);
     for (DOMWindowLifecycleObserver* observer : m_observers)
-        static_cast<DOMWindowLifecycleObserver*>(observer)->didRemoveAllEventListeners(window);
+        observer->didRemoveAllEventListeners(window);
 }
 
 } // namespace blink