Remove the (already disabled) OverflowChangedEvent runtime flag

public/web/WebDOMEvent.h

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 68 matching lines @@
     BLINK_EXPORT bool isMouseEvent() const;
     BLINK_EXPORT bool isMutationEvent() const;
     BLINK_EXPORT bool isKeyboardEvent() const;
     BLINK_EXPORT bool isTextEvent() const;
     BLINK_EXPORT bool isCompositionEvent() const;
     BLINK_EXPORT bool isDragEvent() const;
     BLINK_EXPORT bool isClipboardEvent() const;
     BLINK_EXPORT bool isMessageEvent() const;
     BLINK_EXPORT bool isWheelEvent() const;
     BLINK_EXPORT bool isBeforeTextInsertedEvent() const;
-    BLINK_EXPORT bool isOverflowEvent() const;
     BLINK_EXPORT bool isPageTransitionEvent() const;
     BLINK_EXPORT bool isPopStateEvent() const;
     BLINK_EXPORT bool isProgressEvent() const;
     BLINK_EXPORT bool isXMLHttpRequestProgressEvent() const;
 
 #if BLINK_IMPLEMENTATION
     WebDOMEvent(const PassRefPtrWillBeRawPtr<Event>&);
     operator PassRefPtrWillBeRawPtr<Event>() const;
 #endif
 
@@ skipping 25 matching lines @@
         return static_cast<const T*>(m_private.get());
     }
 #endif
 
     WebPrivatePtr<Event> m_private;
 };
 
 } // namespace blink
 
 #endif