Cleanup unused methods and return values in FWL code.

xfa/fwl/theme/cfwl_scrollbartp.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_SCROLLBARTP_H_
 #define XFA_FWL_THEME_CFWL_SCROLLBARTP_H_
 
 #include <memory>
 
 #include "xfa/fwl/theme/cfwl_widgettp.h"
 
 class CFWL_ScrollBarTP : public CFWL_WidgetTP {
  public:
   CFWL_ScrollBarTP();
   ~CFWL_ScrollBarTP() override;
 
   // CFWL_WidgetTP
   bool IsValidWidget(IFWL_Widget* pWidget) override;
   uint32_t SetThemeID(IFWL_Widget* pWidget, uint32_t dwThemeID) override;
-  FX_BOOL DrawBackground(CFWL_ThemeBackground* pParams) override;
+  void DrawBackground(CFWL_ThemeBackground* pParams) override;
   void* GetCapacity(CFWL_ThemePart* pThemePart,
                     CFWL_WidgetCapacity dwCapacity) override;
 
  protected:
   struct SBThemeData {
     FX_ARGB clrPawColorLight[4];
     FX_ARGB clrPawColorDark[4];
     FX_ARGB clrBtnBK[4][2];
     FX_ARGB clrBtnBorder[4];
     FX_ARGB clrTrackBKStart;
@@ skipping 21 matching lines @@
                const CFX_RectF* pRect,
                FX_BOOL bVert,
                FWLTHEME_STATE eState,
                CFX_Matrix* pMatrix = nullptr);
   void SetThemeData(uint32_t dwID);
 
   std::unique_ptr<SBThemeData> m_pThemeData;
 };
 
 #endif  // XFA_FWL_THEME_CFWL_SCROLLBARTP_H_