Convert FWL_ERR into an enum class.

xfa/fwl/core/ifwl_widgetdelegate.h

Index: xfa/fwl/core/ifwl_widgetdelegate.h
diff --git a/xfa/fwl/core/ifwl_widgetdelegate.h b/xfa/fwl/core/ifwl_widgetdelegate.h
index 7fb56d3ba13ae4b74ac15be74321ede695a40ecc..1b807f4b69e93fe9841029339b77f2f61e94ec10 100644
--- a/xfa/fwl/core/ifwl_widgetdelegate.h
+++ b/xfa/fwl/core/ifwl_widgetdelegate.h
@@ -7,6 +7,8 @@
 #ifndef XFA_FWL_CORE_IFWL_WIDGETDELEGATE_H_
 #define XFA_FWL_CORE_IFWL_WIDGETDELEGATE_H_
 
+#include <stdint.h>
+
 #include "xfa/fwl/core/fwl_error.h"
 
 class CFWL_Event;
@@ -18,9 +20,9 @@ class IFWL_WidgetDelegate {
  public:
   virtual ~IFWL_WidgetDelegate() {}
   virtual int32_t OnProcessMessage(CFWL_Message* pMessage) = 0;
-  virtual FWL_ERR OnProcessEvent(CFWL_Event* pEvent) = 0;
-  virtual FWL_ERR OnDrawWidget(CFX_Graphics* pGraphics,
-                               const CFX_Matrix* pMatrix = nullptr) = 0;
+  virtual FWL_Error OnProcessEvent(CFWL_Event* pEvent) = 0;
+  virtual FWL_Error OnDrawWidget(CFX_Graphics* pGraphics,
+                                 const CFX_Matrix* pMatrix = nullptr) = 0;
 };
 
 #endif  // XFA_FWL_CORE_IFWL_WIDGETDELEGATE_H_