Remove CPDF_Object::GetConstString and overrides

core/fpdfapi/fpdf_parser/include/cpdf_string.h

 // Copyright 2016 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_FPDFAPI_FPDF_PARSER_INCLUDE_CPDF_STRING_H_
 #define CORE_FPDFAPI_FPDF_PARSER_INCLUDE_CPDF_STRING_H_
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_object.h"
 #include "core/fxcrt/include/fx_string.h"
 #include "core/fxcrt/include/fx_system.h"
 
 class CPDF_String : public CPDF_Object {
  public:
   CPDF_String();
   CPDF_String(const CFX_ByteString& str, FX_BOOL bHex);
   explicit CPDF_String(const CFX_WideString& str);
 
   // CPDF_Object.
   Type GetType() const override;
   CPDF_Object* Clone(FX_BOOL bDirect = FALSE) const override;
   CFX_ByteString GetString() const override;
-  CFX_ByteStringC GetConstString() const override;
   CFX_WideString GetUnicodeText() const override;
   void SetString(const CFX_ByteString& str) override;
   bool IsString() const override;
   CPDF_String* AsString() override;
   const CPDF_String* AsString() const override;
 
   FX_BOOL IsHex() const { return m_bHex; }
 
  protected:
   ~CPDF_String() override;
 
   CFX_ByteString m_String;
   FX_BOOL m_bHex;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PARSER_INCLUDE_CPDF_STRING_H_