Convert FWL_ERR into an enum class.

xfa/fwl/core/fwl_error.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_CORE_FWL_ERROR_H_
 #define XFA_FWL_CORE_FWL_ERROR_H_
 
-#include <stdint.h>
-
-typedef int32_t FWL_ERR;
-
-#define FWL_ERR_Succeeded 0
-#define FWL_ERR_Indefinite -1
-#define FWL_ERR_Parameter_Invalid -100
-#define FWL_ERR_Property_Invalid -200
-#define FWL_ERR_Intermediate_Value__Invalid -300
-#define FWL_ERR_Method_Not_Supported -400
-#define FWL_ERR_Out_Of_Memory -500
+enum class FWL_Error {
+  Succeeded = 0,
+  Indefinite,
+  ParameterInvalid,
+  PropertyInvalid,
+  IntermediateValueInvalid,
+  MethodNotSupported,
+  OutOfMemory
+};
 
 #endif  // XFA_FWL_CORE_FWL_ERROR_H_