Use override in more classes in core/

core/src/fxcrt/fxcrt_windows.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 CORE_SRC_FXCRT_FXCRT_WINDOWS_H_
 #define CORE_SRC_FXCRT_FXCRT_WINDOWS_H_
 
 #include "extension.h"
 
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 class CFXCRT_FileAccess_Win64 : public IFXCRT_FileAccess {
  public:
   CFXCRT_FileAccess_Win64();
-  virtual ~CFXCRT_FileAccess_Win64();
-  virtual FX_BOOL Open(const CFX_ByteStringC& fileName, FX_DWORD dwMode);
-  virtual FX_BOOL Open(const CFX_WideStringC& fileName, FX_DWORD dwMode);
-  virtual void Close();
-  virtual void Release();
-  virtual FX_FILESIZE GetSize() const;
-  virtual FX_FILESIZE GetPosition() const;
-  virtual FX_FILESIZE SetPosition(FX_FILESIZE pos);
-  virtual size_t Read(void* pBuffer, size_t szBuffer);
-  virtual size_t Write(const void* pBuffer, size_t szBuffer);
-  virtual size_t ReadPos(void* pBuffer, size_t szBuffer, FX_FILESIZE pos);
-  virtual size_t WritePos(const void* pBuffer,
-                          size_t szBuffer,
-                          FX_FILESIZE pos);
-  virtual FX_BOOL Flush();
-  virtual FX_BOOL Truncate(FX_FILESIZE szFile);
+  ~CFXCRT_FileAccess_Win64() override;
+
+  // IFXCRT_FileAccess
+  FX_BOOL Open(const CFX_ByteStringC& fileName, FX_DWORD dwMode) override;
+  FX_BOOL Open(const CFX_WideStringC& fileName, FX_DWORD dwMode) override;
+  void Close() override;
+  void Release() override;
+  FX_FILESIZE GetSize() const override;
+  FX_FILESIZE GetPosition() const override;
+  FX_FILESIZE SetPosition(FX_FILESIZE pos) override;
+  size_t Read(void* pBuffer, size_t szBuffer) override;
+  size_t Write(const void* pBuffer, size_t szBuffer) override;
+  size_t ReadPos(void* pBuffer, size_t szBuffer, FX_FILESIZE pos) override;
+  size_t WritePos(const void* pBuffer,
+                  size_t szBuffer,
+                  FX_FILESIZE pos) override;
+  FX_BOOL Flush() override;
+  FX_BOOL Truncate(FX_FILESIZE szFile) override;
 
  protected:
   void* m_hFile;
 };
 #endif
 
 #endif  // CORE_SRC_FXCRT_FXCRT_WINDOWS_H_