Move the message definitions to their own files.

xfa/fwl/core/ifwl_checkbox.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_checkbox.h"
 
 #include <algorithm>
 
 #include "third_party/base/ptr_util.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_msgmouse.h"
 #include "xfa/fwl/core/cfwl_themebackground.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_checkbox.h"
 #include "xfa/fwl/core/ifwl_themeprovider.h"
 
 namespace {
 
@@ skipping 474 matching lines @@
 void IFWL_CheckBox::OnKeyDown(CFWL_MsgKey* pMsg) {
   if (pMsg->m_dwKeyCode == FWL_VKEY_Tab) {
     DispatchKeyEvent(pMsg);
     return;
   }
   if (pMsg->m_dwKeyCode == FWL_VKEY_Return ||
       pMsg->m_dwKeyCode == FWL_VKEY_Space) {
     NextStates();
   }
 }