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

core/fxcrt/include/fx_string.h

 // 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
 
 #ifndef CORE_FXCRT_INCLUDE_FX_STRING_H_
 #define CORE_FXCRT_INCLUDE_FX_STRING_H_
 
 #include <stdint.h>  // For intptr_t.
@@ skipping 81 matching lines @@
 
   const uint8_t* raw_str() const { return m_Ptr; }
   const FX_CHAR* c_str() const {
     return reinterpret_cast<const FX_CHAR*>(m_Ptr);
   }
 
   FX_STRSIZE GetLength() const { return m_Length; }
   bool IsEmpty() const { return m_Length == 0; }
 
   uint8_t GetAt(FX_STRSIZE index) const { return m_Ptr[index]; }
+  FX_CHAR CharAt(FX_STRSIZE index) const {
+    return static_cast<FX_CHAR>(m_Ptr[index]);
+  }
 
   FX_STRSIZE Find(FX_CHAR ch) const {
     const uint8_t* found =
         static_cast<const uint8_t*>(memchr(m_Ptr, ch, m_Length));
     return found ? found - m_Ptr : -1;
   }
 
   CFX_ByteStringC Mid(FX_STRSIZE index, FX_STRSIZE count = -1) const {
     if (index < 0) {
       index = 0;
@@ skipping 568 matching lines @@
 }
 
 FX_FLOAT FX_atof(const CFX_ByteStringC& str);
 inline FX_FLOAT FX_atof(const CFX_WideStringC& wsStr) {
   return FX_atof(FX_UTF8Encode(wsStr.c_str(), wsStr.GetLength()).c_str());
 }
 void FX_atonum(const CFX_ByteStringC& str, FX_BOOL& bInteger, void* pData);
 FX_STRSIZE FX_ftoa(FX_FLOAT f, FX_CHAR* buf);
 
 #endif  // CORE_FXCRT_INCLUDE_FX_STRING_H_