Move the message definitions to their own files.

xfa/fwl/core/ifwl_datetimepicker.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_datetimepicker.h"
 
 #include "third_party/base/ptr_util.h"
-#include "xfa/fwl/core/cfwl_message.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_widgetmgr.h"
 #include "xfa/fwl/core/fwl_noteimp.h"
 #include "xfa/fwl/core/ifwl_formproxy.h"
 #include "xfa/fwl/core/ifwl_spinbutton.h"
 #include "xfa/fwl/core/ifwl_themeprovider.h"
 
 namespace {
 
 const int kDateTimePickerWidth = 100;
@@ skipping 658 matching lines @@
   return m_iCurDay;
 }
 
 int32_t IFWL_DateTimePicker::GetCurMonth(IFWL_Widget* pWidget) {
   return m_iCurMonth;
 }
 
 int32_t IFWL_DateTimePicker::GetCurYear(IFWL_Widget* pWidget) {
   return m_iCurYear;
 }