Move the message definitions to their own files.

xfa/fwl/core/ifwl_comboboxproxy.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_IFWL_COMBOBOXPROXY_H_
 #define XFA_FWL_CORE_IFWL_COMBOBOXPROXY_H_
 
 #include "xfa/fwl/core/ifwl_formproxy.h"
 
 class IFWL_ComboBox;
 
 class IFWL_ComboBoxProxy : public IFWL_FormProxy {
  public:
   IFWL_ComboBoxProxy(IFWL_ComboBox* pCombobBox,
                      const IFWL_App* app,
                      std::unique_ptr<CFWL_WidgetProperties> properties,
                      IFWL_Widget* pOuter);
   ~IFWL_ComboBoxProxy() override;
 
   // IFWL_FormProxy
   void OnProcessMessage(CFWL_Message* pMessage) override;
   void OnDrawWidget(CFX_Graphics* pGraphics,
                     const CFX_Matrix* pMatrix) override;
 
   void Reset() { m_bLButtonUpSelf = false; }
 
  private:
-  void OnLButtonDown(CFWL_MsgMouse* pMsg);
-  void OnLButtonUp(CFWL_MsgMouse* pMsg);
-  void OnFocusChanged(CFWL_MsgKillFocus* pMsg, bool bSet);
+  void OnLButtonDown(CFWL_Message* pMsg);
+  void OnLButtonUp(CFWL_Message* pMsg);
+  void OnFocusChanged(CFWL_Message* pMsg, bool bSet);
 
   bool m_bLButtonDown;
   bool m_bLButtonUpSelf;
   IFWL_ComboBox* m_pComboBox;
 };
 
 #endif  // XFA_FWL_CORE_IFWL_COMBOBOXPROXY_H_