Cleanup FWL Event and Message code.

xfa/fwl/core/cfwl_message.cpp

 // 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
 
 #include "xfa/fwl/core/cfwl_message.h"
 
-CFWL_Message::CFWL_Message()
-    : m_pSrcTarget(nullptr), m_pDstTarget(nullptr), m_dwExtend(0) {}
+CFWL_Message::CFWL_Message(CFWL_MessageType type)
+    : m_pSrcTarget(nullptr),
+      m_pDstTarget(nullptr),
+      m_dwExtend(0),
+      m_type(type) {}
 
 CFWL_Message::~CFWL_Message() {}
 
 std::unique_ptr<CFWL_Message> CFWL_Message::Clone() {
   return nullptr;
 }
-
-CFWL_MessageType CFWL_Message::GetClassID() const {
-  return CFWL_MessageType::None;
-}