Add FX_OVERRIDE and use it for virtual functions of FX_FINAL classes.

fpdfsdk/src/fpdfsave.cpp

 // 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
 
 #include "../include/fsdk_define.h"
 #include "../include/fpdfsave.h"
 #include "../include/fpdfedit.h"
 #if _FX_OS_ == _FX_ANDROID_
 #include "time.h"
 #else
 #include <ctime>
 #endif
 
 class CFX_IFileWrite FX_FINAL : public IFX_StreamWrite
 {
         
 public:
         CFX_IFileWrite();
         FX_BOOL                         Init( FPDF_FILEWRITE * pFileWriteStruct );
-        virtual FX_BOOL         WriteBlock(const void* pData, size_t size);
-        virtual void            Release(){};
+        virtual FX_BOOL         WriteBlock(const void* pData, size_t size) FX_OVERRIDE;
+        virtual void            Release() FX_OVERRIDE {}
         
 protected:
         FPDF_FILEWRITE*         m_pFileWriteStruct;
 };
 
 CFX_IFileWrite::CFX_IFileWrite()
 {
         m_pFileWriteStruct = NULL;
 }
 
@@ skipping 53 matching lines @@
 {
         return _FPDF_Doc_Save(document, pFileWrite, flags, FALSE , 0);
 }
 
 
 DLLEXPORT FPDF_BOOL STDCALL FPDF_SaveWithVersion(       FPDF_DOCUMENT document,FPDF_FILEWRITE * pFileWrite,
         FPDF_DWORD flags, int fileVersion)
 {
         return _FPDF_Doc_Save(document, pFileWrite, flags, TRUE , fileVersion);
 }