Convert ReplaceStringPlaceholders(std::string...) to take a

app/l10n_util.cc

Index: app/l10n_util.cc
diff --git a/app/l10n_util.cc b/app/l10n_util.cc
index 854d0a09d05bad148e5325b3979d078e05894988..c04d3d549d7adb3ea097063f42be623e04d9e53f 100644
--- a/app/l10n_util.cc
+++ b/app/l10n_util.cc
@@ -525,6 +525,10 @@ static string16 GetStringF(int message_id,
                            const string16& c,
                            const string16& d,
                            std::vector<size_t>* offsets) {
+  // TODO(tc): We could save a string copy if we got the raw string as
+  // a StringPiece and were able to call ReplaceStringPlaceholders with
+  // a StringPiece format string and string16 substitution strings.  In
+  // practice, the strings should be relatively short.
   ResourceBundle& rb = ResourceBundle::GetSharedInstance();
   const string16& format_string = rb.GetLocalizedString(message_id);
   std::vector<string16> subst;