Move the message definitions to their own files.

xfa/fwl/core/ifwl_datetimeedit.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_datetimeedit.h"
 
 #include "third_party/base/ptr_util.h"
+#include "xfa/fwl/core/cfwl_msgmouse.h"
 #include "xfa/fwl/core/cfwl_widgetmgr.h"
 #include "xfa/fwl/core/ifwl_datetimepicker.h"
 
 IFWL_DateTimeEdit::IFWL_DateTimeEdit(
     const IFWL_App* app,
     std::unique_ptr<CFWL_WidgetProperties> properties,
     IFWL_Widget* pOuter)
     : IFWL_Edit(app, std::move(properties), pOuter) {}
 
 void IFWL_DateTimeEdit::OnProcessMessage(CFWL_Message* pMessage) {
@@ skipping 29 matching lines @@
     if (pDateTime->IsMonthCalendarVisible()) {
       CFX_RectF rtInvalidate;
       pDateTime->GetWidgetRect(rtInvalidate);
       pDateTime->ShowMonthCalendar(false);
       rtInvalidate.Offset(-rtInvalidate.left, -rtInvalidate.top);
       pDateTime->Repaint(&rtInvalidate);
     }
   }
   IFWL_Edit::OnProcessMessage(pMessage);
 }