Cleanup FWL Event and Message code.

xfa/fwl/core/cfwl_msgkey.h

 // Copyright 2016 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef XFA_FWL_CORE_CFWL_MSGKEY_H_
 #define XFA_FWL_CORE_CFWL_MSGKEY_H_
 
 #include <memory>
 
 #include "xfa/fwl/core/cfwl_message.h"
 
 enum class FWL_KeyCommand { KeyDown, KeyUp, Char };
 
 class CFWL_MsgKey : public CFWL_Message {
  public:
-  CFWL_MsgKey();
+  CFWL_MsgKey(CFWL_Widget* pSrcTarget, CFWL_Widget* pDstTarget);
   ~CFWL_MsgKey() override;
 
   // CFWL_Message
   std::unique_ptr<CFWL_Message> Clone() override;
-  CFWL_MessageType GetClassID() const override;
 
   uint32_t m_dwKeyCode;
   uint32_t m_dwFlags;
   FWL_KeyCommand m_dwCmd;
 };
 
 #endif  // XFA_FWL_CORE_CFWL_MSGKEY_H_