Move more string_util functions to base namespace.

chrome/browser/chromeos/drive/file_system_util.cc

Index: chrome/browser/chromeos/drive/file_system_util.cc
diff --git a/chrome/browser/chromeos/drive/file_system_util.cc b/chrome/browser/chromeos/drive/file_system_util.cc
index d339124e74290ebff3e33bfb71665f682fd583d2..e64dafdb79cd995c0483aa79afdf38eabf5ed690 100644
--- a/chrome/browser/chromeos/drive/file_system_util.cc
+++ b/chrome/browser/chromeos/drive/file_system_util.cc
@@ -248,8 +248,8 @@ std::string UnescapeCacheFileName(const std::string& filename) {
   for (size_t i = 0; i < filename.size(); ++i) {
     char c = filename[i];
     if (c == '%' && i + 2 < filename.length()) {
-      c = (HexDigitToInt(filename[i + 1]) << 4) +
-           HexDigitToInt(filename[i + 2]);
+      c = (base::HexDigitToInt(filename[i + 1]) << 4) +
+          base::HexDigitToInt(filename[i + 2]);
       i += 2;
     }
     unescaped.push_back(c);