Cleanup unused methods and return values in FWL code.

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();
   ~CFWL_ListBoxTP() override;
 
   // CFWL_WidgetTP
+  void Initialize() override;
+  void Finalize() override;
   bool IsValidWidget(IFWL_Widget* pWidget) override;
-  FX_BOOL DrawBackground(CFWL_ThemeBackground* pParams) override;
-  FWL_Error Initialize() override;
-  FWL_Error Finalize() override;
+  void DrawBackground(CFWL_ThemeBackground* pParams) override;
 
  protected:
   void DrawListBoxItem(CFX_Graphics* pGraphics,
                        uint32_t dwStates,
                        const CFX_RectF* prtItem,
                        void* pData = nullptr,
                        CFX_Matrix* pMatrix = nullptr);
 };
 
 #endif  // XFA_FWL_THEME_CFWL_LISTBOXTP_H_