Convert FWL_ERR into an enum class.

xfa/fwl/theme/cfwl_listboxtp.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_THEME_CFWL_LISTBOXTP_H_
 #define XFA_FWL_THEME_CFWL_LISTBOXTP_H_
 
 #include "xfa/fwl/theme/cfwl_widgettp.h"
 
 class CFWL_ListBoxTP : public CFWL_WidgetTP {
  public:
   CFWL_ListBoxTP();
   virtual ~CFWL_ListBoxTP();
   virtual FX_BOOL IsValidWidget(IFWL_Widget* pWidget);
   virtual FX_BOOL DrawBackground(CFWL_ThemeBackground* pParams);
-  virtual FWL_ERR Initialize();
-  virtual FWL_ERR Finalize();
+  virtual FWL_Error Initialize();
+  virtual FWL_Error Finalize();
 
  protected:
   void DrawListBoxItem(CFX_Graphics* pGraphics,
                        uint32_t dwStates,
                        const CFX_RectF* prtItem,
                        void* pData = NULL,
                        CFX_Matrix* pMatrix = NULL);
 };
 
 #endif  // XFA_FWL_THEME_CFWL_LISTBOXTP_H_