We should use UserID object to identify users instead of username.

chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h

Index: chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h
diff --git a/chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h b/chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h
index 8c61b0e1f3b0aca6cd99ee5a6a288b871073e6f7..fc3aa114bf50eb36914b4b1d9fb134ec129a331f 100644
--- a/chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h
+++ b/chrome/browser/chromeos/policy/cloud_external_data_policy_observer.h
@@ -38,11 +38,11 @@ class CloudExternalDataPolicyObserver
    public:
     // Invoked when an external data reference is set for |user_id|.
     virtual void OnExternalDataSet(const std::string& policy,
-                                   const std::string& user_id);
+                                   const user_manager::UserID& user_id);
 
     // Invoked when the external data reference is cleared for |user_id|.
     virtual void OnExternalDataCleared(const std::string& policy,
-                                       const std::string& user_id);
+                                       const user_manager::UserID& user_id);
 
     // Invoked when the external data referenced for |user_id| has been fetched.
     // Failed fetches are retried and the method is called only when a fetch
@@ -50,7 +50,7 @@ class CloudExternalDataPolicyObserver
     // external data reference specifies an invalid URL), the method is not
     // called at all.
     virtual void OnExternalDataFetched(const std::string& policy,
-                                       const std::string& user_id,
+                                       const user_manager::UserID& user_id,
                                        scoped_ptr<std::string> data);
 
    protected:
@@ -72,7 +72,7 @@ class CloudExternalDataPolicyObserver
                const content::NotificationDetails& details) override;
 
   // DeviceLocalAccountPolicyService::Observer:
-  void OnPolicyUpdated(const std::string& user_id) override;
+  void OnPolicyUpdated(const user_manager::UserID& user_id) override;
   void OnDeviceLocalAccountsChanged() override;
 
  private:
@@ -85,20 +85,20 @@ class CloudExternalDataPolicyObserver
   // data fetch currently in progress, emitting a notification that an external
   // data reference has been cleared (if |entry| is NULL) or set (otherwise),
   // starting a new external data fetch in the latter case.
-  void HandleExternalDataPolicyUpdate(const std::string& user_id,
+  void HandleExternalDataPolicyUpdate(const user_manager::UserID& user_id,
                                       const PolicyMap::Entry* entry);
 
-  void OnExternalDataFetched(const std::string& user_id,
+  void OnExternalDataFetched(const user_manager::UserID& user_id,
                              scoped_ptr<std::string> data);
 
   // A map from each device-local account user ID to its current policy map
   // entry for |policy_|.
-  typedef std::map<std::string, PolicyMap::Entry> DeviceLocalAccountEntryMap;
+  typedef std::map<user_manager::UserID, PolicyMap::Entry> DeviceLocalAccountEntryMap;
   DeviceLocalAccountEntryMap device_local_account_entries_;
 
   // A map from each logged-in user to the helper that observes |policy_| in the
   // user's PolicyService.
-  typedef std::map<std::string, linked_ptr<PolicyServiceObserver> >
+  typedef std::map<user_manager::UserID, linked_ptr<PolicyServiceObserver> >
       LoggedInUserObserverMap;
   LoggedInUserObserverMap logged_in_user_observers_;
 
@@ -119,7 +119,7 @@ class CloudExternalDataPolicyObserver
   // invalidating the pointers.
   typedef base::WeakPtrFactory<CloudExternalDataPolicyObserver>
       WeakPtrFactory;
-  typedef std::map<std::string, linked_ptr<WeakPtrFactory> > FetchWeakPtrMap;
+  typedef std::map<user_manager::UserID, linked_ptr<WeakPtrFactory> > FetchWeakPtrMap;
   FetchWeakPtrMap fetch_weak_ptrs_;
 
   base::WeakPtrFactory<CloudExternalDataPolicyObserver> weak_factory_;