Remove CPDF_Object::GetConstString and overrides

core/fpdfapi/fpdf_parser/include/cpdf_reference.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_REFERENCE_H_
 #define CORE_FPDFAPI_FPDF_PARSER_INCLUDE_CPDF_REFERENCE_H_
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_object.h"
 
 class CPDF_IndirectObjectHolder;
 
 class CPDF_Reference : public CPDF_Object {
  public:
   CPDF_Reference(CPDF_IndirectObjectHolder* pDoc, int objnum);
 
   // CPDF_Object.
   Type GetType() const override;
   CPDF_Object* Clone(FX_BOOL bDirect = FALSE) const override;
   CPDF_Object* GetDirect() const override;
   CFX_ByteString GetString() const override;
-  CFX_ByteStringC GetConstString() const override;
   FX_FLOAT GetNumber() const override;
   int GetInteger() const override;
   CPDF_Dictionary* GetDict() const override;
 
   // TODO(weili): check whether GetUnicodeText() and GetArray() are needed.
   bool IsReference() const override;
   CPDF_Reference* AsReference() override;
   const CPDF_Reference* AsReference() const override;
 
   CPDF_IndirectObjectHolder* GetObjList() const { return m_pObjList; }
   uint32_t GetRefObjNum() const { return m_RefObjNum; }
 
   void SetRef(CPDF_IndirectObjectHolder* pDoc, uint32_t objnum);
 
  protected:
   ~CPDF_Reference() override;
   CPDF_Object* SafeGetDirect() const {
     CPDF_Object* obj = GetDirect();
     if (!obj || obj->IsReference())
       return nullptr;
     return obj;
   }
 
   CPDF_IndirectObjectHolder* m_pObjList;
   uint32_t m_RefObjNum;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PARSER_INCLUDE_CPDF_REFERENCE_H_