Move more string_util functions to base namespace.

tools/gn/tokenizer.h

Index: tools/gn/tokenizer.h
diff --git a/tools/gn/tokenizer.h b/tools/gn/tokenizer.h
index 497a170a3360265c6331488a986c8cf08dbdc12b..29d107aca9cb69488a6730d94f92ebf8b1a72e82 100644
--- a/tools/gn/tokenizer.h
+++ b/tools/gn/tokenizer.h
@@ -33,12 +33,12 @@ class Tokenizer {
   static bool IsNewline(const base::StringPiece& buffer, size_t offset);
 
   static bool IsIdentifierFirstChar(char c) {
-    return IsAsciiAlpha(c) || c == '_';
+    return base::IsAsciiAlpha(c) || c == '_';
   }
 
   static bool IsIdentifierContinuingChar(char c) {
     // Also allow digits after the first char.
-    return IsIdentifierFirstChar(c) || IsAsciiDigit(c);
+    return IsIdentifierFirstChar(c) || base::IsAsciiDigit(c);
   }
 
  private: