Change userid from a uint32_t to a string guid

components/mus/ws/user_id_tracker.h

 // Copyright 2016 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 COMPONENTS_MUS_WS_USER_ID_TRACKER_H_
 #define COMPONENTS_MUS_WS_USER_ID_TRACKER_H_
 
 #include <stdint.h>
 
 #include <set>
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "components/mus/ws/user_id.h"
 
 namespace mus {
 namespace ws {
 
 class UserIdTrackerObserver;
 
 // Tracks the set of known/valid user ids.
 class UserIdTracker {
  public:
   UserIdTracker();
   ~UserIdTracker();
 
-  bool IsValidUserId(UserId id) const;
+  bool IsValidUserId(const UserId& id) const;
 
-  void SetActiveUserId(UserId id);
-  void AddUserId(UserId id);
-  void RemoveUserId(UserId id);
+  void SetActiveUserId(const UserId& id);
+  void AddUserId(const UserId& id);
+  void RemoveUserId(const UserId& id);
 
   void AddObserver(UserIdTrackerObserver* observer);
   void RemoveObserver(UserIdTrackerObserver* observer);
 
  private:
   using UserIdSet = std::set<UserId>;
 
   base::ObserverList<UserIdTrackerObserver> observers_;
   UserIdSet ids_;
   UserId active_id_;
 
   DISALLOW_COPY_AND_ASSIGN(UserIdTracker);
 };
 
 }  // namespace ws
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_WS_USER_ID_TRACKER_H_