Convert FWL_ERR into an enum class.

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/include/xfa_ffpageview.h"
 
 class CXFA_FFCheckButton : public CXFA_FFField {
  public:
   CXFA_FFCheckButton(CXFA_FFPageView* pPageView, CXFA_WidgetAcc* pDataAcc);
   virtual ~CXFA_FFCheckButton();
   virtual void RenderWidget(CFX_Graphics* pGS,
                             CFX_Matrix* pMatrix = NULL,
                             uint32_t dwStatus = 0,
                             int32_t iRotate = 0);
 
   virtual FX_BOOL LoadWidget();
   virtual FX_BOOL PerformLayout();
   virtual FX_BOOL UpdateFWLData();
   virtual void UpdateWidgetProperty();
   virtual FX_BOOL OnLButtonUp(uint32_t dwFlags, FX_FLOAT fx, FX_FLOAT fy);
   void SetFWLCheckState(XFA_CHECKSTATE eCheckState);
-  virtual int32_t OnProcessMessage(CFWL_Message* pMessage);
-  virtual FWL_ERR OnProcessEvent(CFWL_Event* pEvent);
-  virtual FWL_ERR OnDrawWidget(CFX_Graphics* pGraphics,
-                               const CFX_Matrix* pMatrix = NULL);
+  virtual void OnProcessMessage(CFWL_Message* pMessage);
+  virtual void OnProcessEvent(CFWL_Event* pEvent);
+  virtual void OnDrawWidget(CFX_Graphics* pGraphics,
+                            const CFX_Matrix* pMatrix = NULL);
 
  protected:
   virtual FX_BOOL CommitData();
   virtual FX_BOOL IsDataChanged();
   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_