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

chrome/browser/chromeos/drive/job_scheduler.h

 // Copyright (c) 2012 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 CHROME_BROWSER_CHROMEOS_DRIVE_JOB_SCHEDULER_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_JOB_SCHEDULER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/id_map.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "chrome/browser/chromeos/drive/job_list.h"
 #include "chrome/browser/chromeos/drive/job_queue.h"
 #include "chrome/browser/drive/drive_service_interface.h"
 #include "chrome/browser/drive/drive_uploader.h"
 #include "net/base/network_change_notifier.h"
 
 class PrefService;
 
 namespace base {
 class SeqencedTaskRunner;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace drive {
 
 class EventLogger;
 
 // Priority of a job.  Higher values are lower priority.
 enum ContextType {
   USER_INITIATED,
   BACKGROUND,
   // Indicates the number of values of this enum.
   NUM_CONTEXT_TYPES,
@@ skipping 158 matching lines @@
                           int64 expected_file_size,
                           const base::FilePath& drive_file_path,
                           const base::FilePath& local_file_path,
                           const std::string& content_type,
                           const UploadExistingFileOptions& options,
                           const ClientContext& context,
                           const google_apis::FileResourceCallback& callback);
 
   // Adds AddPermission operation to the queue. |callback| must not be null.
   void AddPermission(const std::string& resource_id,
-                     const std::string& email,
+                     const user_manager::UserID& email,
                      google_apis::drive::PermissionRole role,
                      const google_apis::EntryActionCallback& callback);
 
  private:
   friend class JobSchedulerTest;
 
   enum QueueType {
     METADATA_QUEUE,
     FILE_QUEUE,
     NUM_QUEUES
@@ skipping 182 matching lines @@
 
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<JobScheduler> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(JobScheduler);
 };
 
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_JOB_SCHEDULER_H_