ash: Use enum for SessionController::CycleActiveUser

ash/public/cpp/session_types.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_PUBLIC_CPP_SESSION_TYPES_H_
 #define ASH_PUBLIC_CPP_SESSION_TYPES_H_
 
 namespace ash {
 
 // The index of the user profile to use. The list is always LRU sorted so that
 // index 0 is the currently active user.
 using UserIndex = int;
 
 // Represents possible user adding scenarios.
 enum class AddUserSessionPolicy {
   // Adding a user is allowed.
   ALLOWED,
   // Disallowed due to primary user's policy.
   ERROR_NOT_ALLOWED_PRIMARY_USER,
   // Disallowed due to no eligible users.
   ERROR_NO_ELIGIBLE_USERS,
   // Disallowed due to reaching maximum supported user.
   ERROR_MAXIMUM_USERS_REACHED,
 };
 
+// Defines the cycle direction for |CycleActiveUser|.
+enum class CycleUserDirection {
+  NEXT = 0,  // Cycle to the next user.
+  PREVIOUS,  // Cycle to the previous user.
+};
+
 }  // namespace ash
 
 #endif  // ASH_PUBLIC_CPP_SESSION_TYPES_H_