Implement IsAsciiUpper and IsAsciiLower in base/strings/string_util.h

sandbox/win/src/win_utils.cc

Index: sandbox/win/src/win_utils.cc
diff --git a/sandbox/win/src/win_utils.cc b/sandbox/win/src/win_utils.cc
index 178fd91592579f37caa8a719b562775c5d59d6d4..1425f856eeb4c179dc2f1b151fe512098baabe5f 100644
--- a/sandbox/win/src/win_utils.cc
+++ b/sandbox/win/src/win_utils.cc
@@ -92,8 +92,7 @@ bool StartsWithDriveLetter(const base::string16& path) {
   if (path[1] != L':' || path[2] != L'\\')
     return false;
 
-  return (path[0] >= 'a' && path[0] <= 'z') ||
-         (path[0] >= 'A' && path[0] <= 'Z');
+  return base::IsAsciiAlpha(path[0]);
 }
 
 const wchar_t kNTDotPrefix[] = L"\\\\.\\";