Change IFWL_Widget to store a single delegate.

xfa/fxfa/app/xfa_ffcheckbutton.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_FXFA_APP_XFA_FFCHECKBUTTON_H_
 #define XFA_FXFA_APP_XFA_FFCHECKBUTTON_H_
 
 #include "xfa/fxfa/app/xfa_fffield.h"
 #include "xfa/fxfa/xfa_ffpageview.h"
 
 class CXFA_FFCheckButton : public CXFA_FFField {
  public:
   CXFA_FFCheckButton(CXFA_FFPageView* pPageView, CXFA_WidgetAcc* pDataAcc);
   ~CXFA_FFCheckButton() override;
 
   // CXFA_FFField
   void RenderWidget(CFX_Graphics* pGS,
                     CFX_Matrix* pMatrix,
                     uint32_t dwStatus) override;
 
   FX_BOOL LoadWidget() override;
   FX_BOOL PerformLayout() override;
   FX_BOOL UpdateFWLData() override;
   void UpdateWidgetProperty() override;
   FX_BOOL OnLButtonUp(uint32_t dwFlags, FX_FLOAT fx, FX_FLOAT fy) override;
-  void OnProcessMessage(CFWL_Message* pMessage) override;
-  void OnProcessEvent(CFWL_Event* pEvent) override;
-  void OnDrawWidget(CFX_Graphics* pGraphics,
-                    const CFX_Matrix* pMatrix = nullptr) override;
 
   void SetFWLCheckState(XFA_CHECKSTATE eCheckState);
 
  protected:
   FX_BOOL CommitData() override;
   FX_BOOL IsDataChanged() override;
 
   void CapLeftRightPlacement(CXFA_Margin mgCap);
   void AddUIMargin(int32_t iCapPlacement);
   XFA_CHECKSTATE FWLState2XFAState();
-  IFWL_WidgetDelegate* m_pOldDelegate;
   CFX_RectF m_rtCheckBox;
 };
 
 #endif  // XFA_FXFA_APP_XFA_FFCHECKBUTTON_H_