Translate: Move label parsing logic into common code.

app/l10n_util_mac.mm

Index: app/l10n_util_mac.mm
diff --git a/app/l10n_util_mac.mm b/app/l10n_util_mac.mm
index 9861f14d5e1b8d5f7ac8e1d730cd8b5123ab1d08..3841490e158c77dbb8050cdbfc553444626d5f7c 100644
--- a/app/l10n_util_mac.mm
+++ b/app/l10n_util_mac.mm
@@ -118,6 +118,14 @@ NSString* GetNSStringF(int message_id,
                                                              a, b, c, d));
 }
 
+NSString* GetNSStringF(int message_id,
+                       const string16& a,
+                       const string16& b,
+                       std::vector<size_t>* offsets) {
+  return base::SysUTF16ToNSString(l10n_util::GetStringFUTF16(message_id,
+                                                             a, b, offsets));
+}
+
 NSString* GetNSStringWithFixup(int message_id) {
   return FixUpWindowsStyleLabel(l10n_util::GetStringUTF16(message_id));
 }