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

chrome/browser/chromeos/drive/job_scheduler.h

Index: chrome/browser/chromeos/drive/job_scheduler.h
diff --git a/chrome/browser/chromeos/drive/job_scheduler.h b/chrome/browser/chromeos/drive/job_scheduler.h
index 40a2d61b07e4d2d62013163283d6a1728be7a98e..b219cb724ec7aeacf7f10af9f3a2513795a12413 100644
--- a/chrome/browser/chromeos/drive/job_scheduler.h
+++ b/chrome/browser/chromeos/drive/job_scheduler.h
@@ -23,6 +23,10 @@ namespace base {
 class SeqencedTaskRunner;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace drive {
 
 class EventLogger;
@@ -201,7 +205,7 @@ class JobScheduler
 
   // 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);