Move the message definitions to their own files.

xfa/fwl/core/ifwl_combolist.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/ifwl_combolist.h"
 
 #include "third_party/base/ptr_util.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/ifwl_combobox.h"
 #include "xfa/fwl/core/ifwl_comboedit.h"
 
 IFWL_ComboList::IFWL_ComboList(
     const IFWL_App* app,
     std::unique_ptr<CFWL_WidgetProperties> properties,
     IFWL_Widget* pOuter)
     : IFWL_ListBox(app, std::move(properties), pOuter), m_bNotifyOwner(true) {
   ASSERT(pOuter);
 }
@@ skipping 245 matching lines @@
       CFX_RectF rtInvalidate;
       rtInvalidate.Set(0, 0, m_pProperties->m_rtWidget.width,
                        m_pProperties->m_rtWidget.height);
       Repaint(&rtInvalidate);
       break;
     }
     default:
       break;
   }
 }