Convert FWL_ERR into an enum class.

xfa/fwl/core/fwl_appimp.h

Index: xfa/fwl/core/fwl_appimp.h
diff --git a/xfa/fwl/core/fwl_appimp.h b/xfa/fwl/core/fwl_appimp.h
index 8743b54a43ea3f2dd3f50bd8c85b7266ed885809..dda235eda9178a8c921aba1361873ce67dc39c4f 100644
--- a/xfa/fwl/core/fwl_appimp.h
+++ b/xfa/fwl/core/fwl_appimp.h
@@ -26,13 +26,13 @@ class CFWL_AppImp {
   IFWL_App* GetInterface() const { return m_pIface; }
   CFWL_NoteDriver* GetNoteDriver() const { return m_pNoteDriver.get(); }
 
-  virtual FWL_ERR Initialize();
-  virtual FWL_ERR Finalize();
+  virtual FWL_Error Initialize();
+  virtual FWL_Error Finalize();
   virtual IFWL_AdapterNative* GetAdapterNative() const;
   virtual IFWL_WidgetMgr* GetWidgetMgr() const;
   virtual IFWL_ThemeProvider* GetThemeProvider() const;
-  virtual FWL_ERR SetThemeProvider(IFWL_ThemeProvider* pThemeProvider);
-  virtual FWL_ERR Exit(int32_t iExitCode = 0);
+  virtual FWL_Error SetThemeProvider(IFWL_ThemeProvider* pThemeProvider);
+  virtual FWL_Error Exit(int32_t iExitCode = 0);
 
  protected:
   IFWL_AdapterNative* const m_pAdapterNative;