Cleanup unused methods and return values in FWL code.

xfa/fwl/theme/cfwl_comboboxtp.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_COMBOBOXTP_H_
 #define XFA_FWL_THEME_CFWL_COMBOBOXTP_H_
 
 #include "xfa/fwl/theme/cfwl_widgettp.h"
 
 class CFWL_ComboBoxTP : public CFWL_WidgetTP {
  public:
   CFWL_ComboBoxTP();
   ~CFWL_ComboBoxTP() override;
 
   // CFWL_WidgetTP
   bool IsValidWidget(IFWL_Widget* pWidget) override;
-  FX_BOOL DrawBackground(CFWL_ThemeBackground* pParams) override;
+  void DrawBackground(CFWL_ThemeBackground* pParams) override;
   void* GetCapacity(CFWL_ThemePart* pThemePart,
                     CFWL_WidgetCapacity dwCapacity) override;
 
  protected:
   void DrawDropDownButton(CFWL_ThemeBackground* pParams,
                           uint32_t dwStates,
                           CFX_Matrix* pMatrix);
   void DrawStrethHandler(CFWL_ThemeBackground* pParams,
                          uint32_t dwStates,
                          CFX_Matrix* pMatrix);
 };
 
 #endif  // XFA_FWL_THEME_CFWL_COMBOBOXTP_H_