Convert FWL_ERR into an enum class.

xfa/fwl/theme/cfwl_listboxtp.cpp

Index: xfa/fwl/theme/cfwl_listboxtp.cpp
diff --git a/xfa/fwl/theme/cfwl_listboxtp.cpp b/xfa/fwl/theme/cfwl_listboxtp.cpp
index f1a017ab706051014b83f5cbd5c234f5cebfb7fd..5bab1b09e5d608fa341b0879c7a3a508e2f44b21 100644
--- a/xfa/fwl/theme/cfwl_listboxtp.cpp
+++ b/xfa/fwl/theme/cfwl_listboxtp.cpp
@@ -66,11 +66,11 @@ FX_BOOL CFWL_ListBoxTP::DrawBackground(CFWL_ThemeBackground* pParams) {
   }
   return TRUE;
 }
-FWL_ERR CFWL_ListBoxTP::Initialize() {
+FWL_Error CFWL_ListBoxTP::Initialize() {
   InitTTO();
   return CFWL_WidgetTP::Initialize();
 }
-FWL_ERR CFWL_ListBoxTP::Finalize() {
+FWL_Error CFWL_ListBoxTP::Finalize() {
   FinalizeTTO();
   return CFWL_WidgetTP::Finalize();
 }