Extern in .cpp files is a code smell.

core/src/fpdfapi/fpdf_font/font_int.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_FPDFAPI_FPDF_FONT_FONT_INT_H_
 #define CORE_SRC_FPDFAPI_FPDF_FONT_FONT_INT_H_
 
 #include <map>
 
 #include "../../../include/fxcrt/fx_basic.h"
 #include "../../../include/fpdfapi/fpdf_resource.h"
 
 class CPDF_CID2UnicodeMap;
 class CPDF_CMap;
 class CPDF_Font;
 class CPDF_Stream;
 
 typedef void* FXFT_Library;
 
+short TT2PDF(int m, FXFT_Face face);
+FX_BOOL FT_UseTTCharmap(FXFT_Face face, int platform_id, int encoding_id);
+
 class CPDF_CMapManager {
  public:
   CPDF_CMapManager();
   ~CPDF_CMapManager();
   void* GetPackage(FX_BOOL bPrompt);
   CPDF_CMap* GetPredefinedCMap(const CFX_ByteString& name, FX_BOOL bPrompt);
   CPDF_CID2UnicodeMap* GetCID2UnicodeMap(int charset, FX_BOOL bPrompt);
   void ReloadAll();
 
  private:
@@ skipping 144 matching lines @@
   CPDF_CID2UnicodeMap* m_pBaseMap;
   CFX_WideTextBuf m_MultiCharBuf;
 };
 class CPDF_FontCharMap : public CFX_CharMap {
  public:
   CPDF_FontCharMap(CPDF_Font* pFont);
   CPDF_Font* m_pFont;
 };
 
 #endif  // CORE_SRC_FPDFAPI_FPDF_FONT_FONT_INT_H_