Fix compilation under chromium checkouts.

core/include/fxcrt/fx_system.h

Index: core/include/fxcrt/fx_system.h
diff --git a/core/include/fxcrt/fx_system.h b/core/include/fxcrt/fx_system.h
index 50d3344a8998d297003bf817903910262431483d..e1e957a52d4d75da55be25374da955c94aec2650 100644
--- a/core/include/fxcrt/fx_system.h
+++ b/core/include/fxcrt/fx_system.h
@@ -191,16 +191,8 @@ void FXSYS_vsnprintf(char *str, size_t size, const char* fmt, va_list ap);
 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