Revert of Move JoinString to the base namespace

chrome/browser/chromeos/login/session/user_session_manager.cc

Index: chrome/browser/chromeos/login/session/user_session_manager.cc
diff --git a/chrome/browser/chromeos/login/session/user_session_manager.cc b/chrome/browser/chromeos/login/session/user_session_manager.cc
index 0a02b539fc9aa28117f98c2bf7e8fcd05bca168a..af0f02665c5c5545eb8ff6e88531d4ebbdcbdf71 100644
--- a/chrome/browser/chromeos/login/session/user_session_manager.cc
+++ b/chrome/browser/chromeos/login/session/user_session_manager.cc
@@ -156,7 +156,7 @@
   // Save the input methods in the user's preferences.
   StringPrefMember language_preload_engines;
   language_preload_engines.Init(prefs::kLanguagePreloadEngines, prefs);
-  language_preload_engines.SetValue(base::JoinString(input_method_ids, ","));
+  language_preload_engines.SetValue(JoinString(input_method_ids, ','));
   BootTimesRecorder::Get()->AddLoginTimeMarker("IMEStarted", false);
 
   // Second, we'll set kLanguagePreferredLanguages.
@@ -184,7 +184,7 @@
 
   // Save the preferred languages in the user's preferences.
   prefs->SetString(prefs::kLanguagePreferredLanguages,
-                   base::JoinString(language_codes, ","));
+                   JoinString(language_codes, ','));
 
   // Indicate that we need to merge the syncable input methods when we sync,
   // since we have not applied the synced prefs before.