Enumerate the return value of dispatchEvent so it is clear.

third_party/WebKit/Source/core/events/MouseEvent.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 117 matching lines @@
 };
 
 class MouseEventDispatchMediator final : public EventDispatchMediator {
 public:
     static PassRefPtrWillBeRawPtr<MouseEventDispatchMediator> create(PassRefPtrWillBeRawPtr<MouseEvent>);
 
 private:
     explicit MouseEventDispatchMediator(PassRefPtrWillBeRawPtr<MouseEvent>);
     MouseEvent& event() const;
 
-    bool dispatchEvent(EventDispatcher&) const override;
+    DispatchEventResult dispatchEvent(EventDispatcher&) const override;
 };
 
 DEFINE_EVENT_TYPE_CASTS(MouseEvent);
 
 } // namespace blink
 
 #endif // MouseEvent_h