Extern in .cpp files is a code smell.

core/src/fpdfapi/fpdf_font/fpdf_font_cid.cpp

 // 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
 
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fpdfapi/fpdf_page.h"
 #include "../../../include/fpdfapi/fpdf_resource.h"
 #include "../../../include/fxge/fx_freetype.h"
 #include "../../../include/fxge/fx_ge.h"
 #include "../fpdf_cmaps/cmap_int.h"
 #include "font_int.h"
 
-extern short TT2PDF(int m, FXFT_Face face);
-extern FX_BOOL FT_UseTTCharmap(FXFT_Face face,
-                               int platform_id,
-                               int encoding_id);
-
 CPDF_CMapManager::CPDF_CMapManager() {
   m_bPrompted = FALSE;
   FXSYS_memset(m_CID2UnicodeMaps, 0, sizeof m_CID2UnicodeMaps);
 }
 CPDF_CMapManager::~CPDF_CMapManager() {
   for (const auto& pair : m_CMaps) {
     delete pair.second;
   }
   m_CMaps.clear();
   for (int i = 0; i < FX_ArraySize(m_CID2UnicodeMaps); ++i) {
@@ skipping 1609 matching lines @@
     if (middlecode > CID) {
       end = middle - 1;
     } else if (middlecode < CID) {
       begin = middle + 1;
     } else {
       return &Japan1_VertCIDs[middle].a;
     }
   }
   return NULL;
 }