Move JoinString to the base namespace

chromeos/network/network_change_notifier_chromeos.cc

Index: chromeos/network/network_change_notifier_chromeos.cc
diff --git a/chromeos/network/network_change_notifier_chromeos.cc b/chromeos/network/network_change_notifier_chromeos.cc
index 4561091d5214e172a6f53d28e8fac3a998696d6b..52ee616a184938c032d185b6cbc694b5e43e2b66 100644
--- a/chromeos/network/network_change_notifier_chromeos.cc
+++ b/chromeos/network/network_change_notifier_chromeos.cc
@@ -211,9 +211,8 @@ void NetworkChangeNotifierChromeos::UpdateState(
     NET_LOG_EVENT(
         "NCNDefaultDNSServerChanged",
         base::StringPrintf(
-            "%s -> %s",
-            JoinString(dns_servers_, ",").c_str(),
-            JoinString(default_network->dns_servers(), ",").c_str()));
+            "%s -> %s", base::JoinString(dns_servers_, ",").c_str(),
+            base::JoinString(default_network->dns_servers(), ",").c_str()));
     *dns_changed = true;
   }