Move more string_util functions to base namespace.

tools/gn/tokenizer.cc

Index: tools/gn/tokenizer.cc
diff --git a/tools/gn/tokenizer.cc b/tools/gn/tokenizer.cc
index 567fa72b479e92f824e48e43943461a6f9904792..be3223b5e145e48bfc4db5dc6311f88856557b70 100644
--- a/tools/gn/tokenizer.cc
+++ b/tools/gn/tokenizer.cc
@@ -188,7 +188,7 @@ void Tokenizer::AdvanceToNextToken() {
 Token::Type Tokenizer::ClassifyCurrent() const {
   DCHECK(!at_end());
   char next_char = cur_char();
-  if (IsAsciiDigit(next_char))
+  if (base::IsAsciiDigit(next_char))
     return Token::INTEGER;
   if (next_char == '"')
     return Token::STRING;
@@ -228,7 +228,7 @@ Token::Type Tokenizer::ClassifyCurrent() const {
       return Token::UNCLASSIFIED_OPERATOR;  // Just the minus before end of
                                             // file.
     char following_char = input_[cur_ + 1];
-    if (IsAsciiDigit(following_char))
+    if (base::IsAsciiDigit(following_char))
       return Token::INTEGER;
     return Token::UNCLASSIFIED_OPERATOR;
   }
@@ -242,7 +242,7 @@ void Tokenizer::AdvanceToEndOfToken(const Location& location,
     case Token::INTEGER:
       do {
         Advance();
-      } while (!at_end() && IsAsciiDigit(cur_char()));
+      } while (!at_end() && base::IsAsciiDigit(cur_char()));
       if (!at_end()) {
         // Require the char after a number to be some kind of space, scope,
         // or operator.