Move more string_util functions to base namespace.

extensions/common/csp_validator.cc

Index: extensions/common/csp_validator.cc
diff --git a/extensions/common/csp_validator.cc b/extensions/common/csp_validator.cc
index ced436e95d6e4896e7b92e6e6c939f208b6830ce..06ea4ef6f3e71f898af4e350d5963cf0ea82c8bb 100644
--- a/extensions/common/csp_validator.cc
+++ b/extensions/common/csp_validator.cc
@@ -83,7 +83,7 @@ bool isNonWildcardTLD(const std::string& url,
     // ":123456" or ":****" as valid, but that does not matter because the
     // relaxing CSP directive will just be ignored by Blink.
     for (size_t i = start_of_port + 1; i < end_of_host; ++i) {
-      is_valid_port = IsAsciiDigit(url[i]) || url[i] == '*';
+      is_valid_port = base::IsAsciiDigit(url[i]) || url[i] == '*';
       if (!is_valid_port)
         break;
     }