Fix a potential integer overflow in TT2PDF().

core/fpdfapi/fpdf_font/fpdf_font.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 "core/fpdfapi/fpdf_font/font_int.h"
 
 #include "core/fpdfapi/fpdf_page/cpdf_pagemodule.h"
 #include "core/fpdfapi/fpdf_page/include/cpdf_form.h"
 #include "core/fpdfapi/fpdf_page/pageint.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_array.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_document.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_name.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_number.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_simple_parser.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_stream_acc.h"
 #include "core/fpdfapi/include/cpdf_modulemgr.h"
 #include "core/fxcrt/include/fx_ext.h"
 #include "core/fxge/include/fx_freetype.h"
+#include "third_party/base/numerics/safe_conversions.h"
 #include "third_party/base/stl_util.h"
 
 int TT2PDF(int m, FXFT_Face face) {
   int upm = FXFT_Get_Face_UnitsPerEM(face);
   if (upm == 0)
     return m;
-  return (m * 1000 + upm / 2) / upm;
+  return pdfium::base::checked_cast<int>(
+      (static_cast<double>(m) * 1000 + upm / 2) / upm);
 }
 
 bool FT_UseTTCharmap(FXFT_Face face, int platform_id, int encoding_id) {
   auto* pCharMap = FXFT_Get_Face_Charmaps(face);
   for (int i = 0; i < FXFT_Get_Face_CharmapCount(face); i++) {
     if (FXFT_Get_Charmap_PlatformID(pCharMap[i]) == platform_id &&
         FXFT_Get_Charmap_EncodingID(pCharMap[i]) == encoding_id) {
       FXFT_Set_Charmap(face, pCharMap[i]);
       return true;
     }
@@ skipping 255 matching lines @@
   }
   if (cid_set) {
     m_pBaseMap = CPDF_ModuleMgr::Get()
                      ->GetPageModule()
                      ->GetFontGlobals()
                      ->m_CMapManager.GetCID2UnicodeMap(cid_set, FALSE);
   } else {
     m_pBaseMap = nullptr;
   }
 }