ash: Use enum for SessionController::CycleActiveUser

ash/common/session/session_controller.cc

Index: ash/common/session/session_controller.cc
diff --git a/ash/common/session/session_controller.cc b/ash/common/session/session_controller.cc
index d108b3349aed0a1996ef0d15aa674b5393c33848..cafed50edd36116302adf2756c53cc40af0bdafb 100644
--- a/ash/common/session/session_controller.cc
+++ b/ash/common/session/session_controller.cc
@@ -73,9 +73,9 @@ void SessionController::SwitchActiveUser(const AccountId& account_id) {
     client_->SwitchActiveUser(account_id);
 }
 
-void SessionController::CycleActiveUser(bool next_user) {
+void SessionController::CycleActiveUser(CycleUserDirection direction) {
   if (client_)
-    client_->CycleActiveUser(next_user);
+    client_->CycleActiveUser(direction);
 }
 
 void SessionController::AddSessionStateObserver(