Convert FWL_ERR into an enum class.

xfa/fwl/core/fwl_timerimp.cpp

Index: xfa/fwl/core/fwl_timerimp.cpp
diff --git a/xfa/fwl/core/fwl_timerimp.cpp b/xfa/fwl/core/fwl_timerimp.cpp
index 8a5f8896f537875c356b2fa372bb4d344b461279..9263fce08501d4fcccd463e65fcef20b8cac024d 100644
--- a/xfa/fwl/core/fwl_timerimp.cpp
+++ b/xfa/fwl/core/fwl_timerimp.cpp
@@ -23,12 +23,14 @@ FWL_HTIMER FWL_StartTimer(IFWL_Timer* pTimer,
   pAdapterTimerMgr->Start(pTimer, dwElapse, hTimer, bImmediately);
   return hTimer;
 }
-int32_t FWL_StopTimer(FWL_HTIMER hTimer) {
+
+FWL_Error FWL_StopTimer(FWL_HTIMER hTimer) {
   IFWL_AdapterNative* pAdapterNative = FWL_GetAdapterNative();
   if (!pAdapterNative)
-    return FWL_ERR_Indefinite;
+    return FWL_Error::Indefinite;
+
   IFWL_AdapterTimerMgr* pAdapterTimerMgr = pAdapterNative->GetTimerMgr();
   if (!pAdapterTimerMgr)
-    return FWL_ERR_Indefinite;
+    return FWL_Error::Indefinite;
   return pAdapterTimerMgr->Stop(hTimer);
 }