Cleanup unused methods and return values in FWL code.

xfa/fwl/theme/cfwl_pushbuttontp.h

Index: xfa/fwl/theme/cfwl_pushbuttontp.h
diff --git a/xfa/fwl/theme/cfwl_pushbuttontp.h b/xfa/fwl/theme/cfwl_pushbuttontp.h
index 053ca28831cd0bfed4d84c3cd0929ff813e80862..317d0d2336f5bc9399eadf39214349ec20fa4247 100644
--- a/xfa/fwl/theme/cfwl_pushbuttontp.h
+++ b/xfa/fwl/theme/cfwl_pushbuttontp.h
@@ -17,13 +17,13 @@ class CFWL_PushButtonTP : public CFWL_WidgetTP {
   ~CFWL_PushButtonTP() override;
 
   // CFWL_WidgetTP
+  void Initialize() override;
+  void Finalize() override;
   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;
-  FWL_Error Initialize() override;
-  FWL_Error Finalize() override;
 
  protected:
   struct PBThemeData {