Make code compile with clang_use_chrome_plugin (part III)

xfa/fxbarcode/datamatrix/BC_ASCIIEncoder.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_FXBARCODE_DATAMATRIX_BC_ASCIIENCODER_H_
 #define XFA_FXBARCODE_DATAMATRIX_BC_ASCIIENCODER_H_
 
 #include "xfa/fxbarcode/datamatrix/BC_Encoder.h"
 
 class CBC_EncoderContext;
 
 class CBC_ASCIIEncoder : public CBC_Encoder {
  public:
   CBC_ASCIIEncoder();
-  virtual ~CBC_ASCIIEncoder();
-  int32_t getEncodingMode();
-  void Encode(CBC_EncoderContext& context, int32_t& e);
+  ~CBC_ASCIIEncoder() override;
+
+  // CBC_Encoder
+  int32_t getEncodingMode() override;
+  void Encode(CBC_EncoderContext& context, int32_t& e) override;
 
  private:
   static FX_WCHAR encodeASCIIDigits(FX_WCHAR digit1,
                                     FX_WCHAR digit2,
                                     int32_t& e);
 };
 
 #endif  // XFA_FXBARCODE_DATAMATRIX_BC_ASCIIENCODER_H_