Include Event.h in fewer header files

Source/core/frame/EventHandlerRegistry.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EventHandlerRegistry_h
 #define EventHandlerRegistry_h
 
-#include "core/events/Event.h"
 #include "core/frame/FrameHost.h"
 #include "wtf/HashCountedSet.h"
 
 namespace WebCore {
 
+class Document;
+class EventTarget;
+
 typedef HashCountedSet<EventTarget*> EventTargetSet;
 
 // Registry for keeping track of event handlers. Note that only handlers on
 // documents that can be rendered or can receive input (i.e., are attached to a
 // FrameHost) are registered here.
 class EventHandlerRegistry FINAL : public NoBaseWillBeGarbageCollectedFinalized<EventHandlerRegistry> {
 public:
     explicit EventHandlerRegistry(FrameHost&);
     virtual ~EventHandlerRegistry();
 
@@ skipping 63 matching lines @@
 
     void checkConsistency() const;
 
     FrameHost& m_frameHost;
     EventTargetSet m_targets[EventHandlerClassCount];
 };
 
 } // namespace WebCore
 
 #endif // EventHandlerRegistry_h