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

net/base/parse_number.cc

Index: net/base/parse_number.cc
diff --git a/net/base/parse_number.cc b/net/base/parse_number.cc
index 365aa350b472c1f58e29903d91943f4fcc69c096..460947f70af7645c3d3e78de4695cdd727c2cf0f 100644
--- a/net/base/parse_number.cc
+++ b/net/base/parse_number.cc
@@ -6,6 +6,7 @@
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 
 namespace net {
 
@@ -51,7 +52,7 @@ bool ParseIntHelper(const base::StringPiece& input,
     return SetError(ParseIntError::FAILED_PARSE, optional_error);
 
   bool starts_with_negative = input[0] == '-';
-  bool starts_with_digit = input[0] >= '0' && input[0] <= '9';
+  bool starts_with_digit = base::IsAsciiDigit(input[0]);
 
   if (!starts_with_digit) {
     if (format == ParseIntFormat::NON_NEGATIVE || !starts_with_negative)