Add CFX_ByteStringC::CharAt() to avoid c_str() and casts

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"
@@ skipping 121 matching lines @@
 
 // Static.
 uint32_t CPDF_ToUnicodeMap::StringToCode(const CFX_ByteStringC& str) {
   int len = str.GetLength();
   if (len == 0)
     return 0;
 
   int result = 0;
   if (str[0] == '<') {
     for (int i = 1; i < len && std::isxdigit(str[i]); ++i)
-      result = result * 16 + FXSYS_toHexDigit(str[i]);
+      result = result * 16 + FXSYS_toHexDigit(str.CharAt(i));
     return result;
   }
 
   for (int i = 0; i < len && std::isdigit(str[i]); ++i)
-    result = result * 10 + FXSYS_toDecimalDigit(static_cast<FX_CHAR>(str[i]));
+    result = result * 10 + FXSYS_toDecimalDigit(str.CharAt(i));
 
   return result;
 }
 
 static CFX_WideString StringDataAdd(CFX_WideString str) {
   CFX_WideString ret;
   int len = str.GetLength();
   FX_WCHAR value = 1;
   for (int i = len - 1; i >= 0; --i) {
     FX_WCHAR ch = str[i] + value;
@@ skipping 135 matching lines @@
   }
   if (cid_set) {
     m_pBaseMap = CPDF_ModuleMgr::Get()
                      ->GetPageModule()
                      ->GetFontGlobals()
                      ->m_CMapManager.GetCID2UnicodeMap(cid_set, FALSE);
   } else {
     m_pBaseMap = NULL;
   }
 }