Fix a bunch of sign mismatch warnings.

core/src/fpdfapi/fpdf_cmaps/fpdf_cmaps.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_resource.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../fpdf_font/font_int.h"
 #include "cmap_int.h"
@@ skipping 161 matching lines @@
         pCur += 3;
       }
     }
     if (pMap->m_UseOffset == 0) {
       return 0;
     }
     pMap = pMap + pMap->m_UseOffset;
   }
   return 0;
 }
-void FPDFAPI_LoadCID2UnicodeMap(int charset,
+void FPDFAPI_LoadCID2UnicodeMap(size_t charset,
                                 const FX_WORD*& pMap,
                                 FX_DWORD& count) {
   CPDF_FontGlobals* pFontGlobals =
       CPDF_ModuleMgr::Get()->GetPageModule()->GetFontGlobals();
   pMap = pFontGlobals->m_EmbeddedToUnicodes[charset].m_pMap;
   count = pFontGlobals->m_EmbeddedToUnicodes[charset].m_Count;
 }