Restore checked strlen conversions.

core/include/fxcrt/fx_system.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 _FX_SYSTEM_H_
 #define _FX_SYSTEM_H_
 #define _FX_WIN32_DESKTOP_              1
 #define _FX_LINUX_DESKTOP_              4
@@ skipping 174 matching lines @@
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 #ifdef _NATIVE_WCHAR_T_DEFINED
 #define FXSYS_wfopen(f, m) _wfopen((const wchar_t*)(f), (const wchar_t*)(m))
 #else
 #define FXSYS_wfopen _wfopen
 #endif
 #else
 FXSYS_FILE* FXSYS_wfopen(FX_LPCWSTR filename, FX_LPCWSTR mode);
 #endif
 
+#ifdef __cplusplus
+} // extern "C"
+#include "../../../third_party/base/numerics/safe_conversions.h"
+#define FXSYS_strlen(ptr) pdfium::base::checked_cast<FX_STRSIZE>(strlen(ptr))
+#define FXSYS_wcslen(ptr) pdfium::base::checked_cast<FX_STRSIZE>(wcslen(ptr))
+extern "C" {
+#else
 #define FXSYS_strlen(ptr) ((FX_STRSIZE)strlen(ptr))
 #define FXSYS_wcslen(ptr) ((FX_STRSIZE)wcslen(ptr))
+#endif
 
 #define FXSYS_wcscmp    wcscmp
 #define FXSYS_wcschr    wcschr
 #define FXSYS_wcsstr    wcsstr
 #define FXSYS_wcsncmp   wcsncmp
 #define FXSYS_vswprintf vswprintf
 #define FXSYS_mbstowcs  mbstowcs
 #define FXSYS_wcstombs  wcstombs
 #define FXSYS_memcmp    memcmp
 #define FXSYS_memcpy    memcpy
@@ skipping 128 matching lines @@
 
 #else  // _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 
 #if !defined(PRIuS)
 #define PRIuS "Iu"
 #endif
 
 #endif
 
 #endif