Use virtual function to retrieve interface pointer

xfa/fxfa/app/xfa_ffcheckbutton.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/fxfa/app/xfa_ffcheckbutton.h"
 
 #include "xfa/fwl/core/cfwl_message.h"
 #include "xfa/fwl/core/cfwl_widgetmgr.h"
@@ skipping 230 matching lines @@
   if (!m_pNormalWidget || !IsButtonDown())
     return FALSE;
 
   SetButtonDown(FALSE);
   CFWL_MsgMouse ms;
   ms.m_dwCmd = FWL_MouseCommand::LeftButtonUp;
   ms.m_dwFlags = dwFlags;
   ms.m_fx = fx;
   ms.m_fy = fy;
   FWLToClient(ms.m_fx, ms.m_fy);
-  ms.m_pDstTarget = m_pNormalWidget->m_pIface;
+  ms.m_pDstTarget = m_pNormalWidget->GetWidget();
   TranslateFWLMessage(&ms);
   return TRUE;
 }
 
 XFA_CHECKSTATE CXFA_FFCheckButton::FWLState2XFAState() {
   uint32_t dwState = m_pNormalWidget->GetStates();
   if (dwState & FWL_STATE_CKB_Checked)
     return XFA_CHECKSTATE_On;
   if (dwState & FWL_STATE_CKB_Neutral)
     return XFA_CHECKSTATE_Neutral;
@@ skipping 63 matching lines @@
     default:
       break;
   }
   m_pOldDelegate->OnProcessEvent(pEvent);
 }
 
 void CXFA_FFCheckButton::OnDrawWidget(CFX_Graphics* pGraphics,
                                       const CFX_Matrix* pMatrix) {
   m_pOldDelegate->OnDrawWidget(pGraphics, pMatrix);
 }