Use virtual function to retrieve interface pointer

xfa/fwl/lightwidget/cfwl_pushbutton.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/lightwidget/cfwl_pushbutton.h"
 
 #include <memory>
 
+IFWL_PushButton* CFWL_PushButton::GetWidget() {
+  return static_cast<IFWL_PushButton*>(m_pIface.get());
+}
+
+const IFWL_PushButton* CFWL_PushButton::GetWidget() const {
+  return static_cast<IFWL_PushButton*>(m_pIface.get());
+}
+
 CFWL_PushButton* CFWL_PushButton::Create() {
   return new CFWL_PushButton;
 }
 
 FWL_Error CFWL_PushButton::Initialize(
     const CFWL_WidgetProperties* pProperties) {
   if (m_pIface)
     return FWL_Error::Indefinite;
   if (pProperties) {
     *m_pProperties = *pProperties;
   }
   std::unique_ptr<IFWL_PushButton> pPushButton(IFWL_PushButton::Create(
       m_pProperties->MakeWidgetImpProperties(&m_buttonData), nullptr));
   FWL_Error ret = pPushButton->Initialize();
   if (ret != FWL_Error::Succeeded) {
     return ret;
   }
-  m_pIface = pPushButton.release();
+  m_pIface = std::move(pPushButton);
   CFWL_Widget::Initialize();
   return FWL_Error::Succeeded;
 }
 
 FWL_Error CFWL_PushButton::GetCaption(CFX_WideString& wsCaption) {
   wsCaption = m_buttonData.m_wsCaption;
   return FWL_Error::Succeeded;
 }
 
 FWL_Error CFWL_PushButton::SetCaption(const CFX_WideStringC& wsCaption) {
@@ skipping 18 matching lines @@
     IFWL_Widget* pWidget,
     CFX_WideString& wsCaption) {
   wsCaption = m_wsCaption;
   return FWL_Error::Succeeded;
 }
 
 CFX_DIBitmap* CFWL_PushButton::CFWL_PushButtonDP::GetPicture(
     IFWL_Widget* pWidget) {
   return m_pBitmap;
 }