Use FXFONT defines in place of integers.

core/fpdfdoc/cpvt_fontmap.cpp

 // 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
 
 #include "core/fpdfdoc/cpvt_fontmap.h"
 
 #include "core/fpdfapi/fpdf_font/include/cpdf_font.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
@@ skipping 70 matching lines @@
   return 0;
 }
 
 int32_t CPVT_FontMap::CharCodeFromUnicode(int32_t nFontIndex, uint16_t word) {
   ASSERT(false);
   return 0;
 }
 
 int32_t CPVT_FontMap::CharSetFromUnicode(uint16_t word, int32_t nOldCharset) {
   ASSERT(false);
-  return 0;
+  return FXFONT_ANSI_CHARSET;
 }