Move the message definitions to their own files.

xfa/fwl/core/ifwl_combobox.cpp

 // Copyright 2014 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/ifwl_combobox.h"
 
 #include "third_party/base/ptr_util.h"
 #include "xfa/fde/cfde_txtedtengine.h"
 #include "xfa/fde/tto/fde_textout.h"
-#include "xfa/fwl/core/cfwl_message.h"
+#include "xfa/fwl/core/cfwl_msgkey.h"
+#include "xfa/fwl/core/cfwl_msgkillfocus.h"
+#include "xfa/fwl/core/cfwl_msgmouse.h"
+#include "xfa/fwl/core/cfwl_msgsetfocus.h"
 #include "xfa/fwl/core/cfwl_themebackground.h"
 #include "xfa/fwl/core/cfwl_themepart.h"
 #include "xfa/fwl/core/cfwl_themetext.h"
 #include "xfa/fwl/core/cfwl_widgetmgr.h"
 #include "xfa/fwl/core/fwl_noteimp.h"
 #include "xfa/fwl/core/ifwl_app.h"
 #include "xfa/fwl/core/ifwl_formproxy.h"
 #include "xfa/fwl/core/ifwl_themeprovider.h"
 
 IFWL_ComboBox::IFWL_ComboBox(const IFWL_App* app,
@@ skipping 1116 matching lines @@
       else
         iCurSel++;
     }
     m_iCurSel = iCurSel;
     SyncEditText(m_iCurSel);
     return;
   }
   if (m_pEdit)
     m_pEdit->GetDelegate()->OnProcessMessage(pMsg);
 }