Use virtual function to retrieve interface pointer

xfa/fwl/lightwidget/cfwl_datetimepicker.h

 // 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
 
 #ifndef XFA_FWL_LIGHTWIDGET_CFWL_DATETIMEPICKER_H_
 #define XFA_FWL_LIGHTWIDGET_CFWL_DATETIMEPICKER_H_
 
 #include "xfa/fwl/basewidget/ifwl_datetimepicker.h"
 #include "xfa/fwl/lightwidget/cfwl_widget.h"
 
 class CFWL_DateTimePicker : public CFWL_Widget {
  public:
   static CFWL_DateTimePicker* Create();
 
+  IFWL_DateTimePicker* GetWidget() override;
+  const IFWL_DateTimePicker* GetWidget() const override;
+
   FWL_Error Initialize(const CFWL_WidgetProperties* pProperties = nullptr);
   FWL_Error SetToday(int32_t iYear, int32_t iMonth, int32_t iDay);
   FWL_Error GetEditText(CFX_WideString& wsText);
   FWL_Error SetEditText(const CFX_WideString& wsText);
   int32_t CountSelRanges();
   int32_t GetSelRange(int32_t nIndex, int32_t& nStart);
   FWL_Error GetCurSel(int32_t& iYear, int32_t& iMonth, int32_t& iDay);
   FWL_Error SetCurSel(int32_t iYear, int32_t iMonth, int32_t iDay);
   FX_BOOL CanUndo();
   FX_BOOL CanRedo();
@@ skipping 33 matching lines @@
     CFX_WideString m_wsData;
   };
 
   CFWL_DateTimePicker();
   ~CFWL_DateTimePicker() override;
 
   CFWL_DateTimePickerDP m_DateTimePickerDP;
 };
 
 #endif  // XFA_FWL_LIGHTWIDGET_CFWL_DATETIMEPICKER_H_