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

chrome/browser/chromeos/drive/file_system.cc

Index: chrome/browser/chromeos/drive/file_system.cc
diff --git a/chrome/browser/chromeos/drive/file_system.cc b/chrome/browser/chromeos/drive/file_system.cc
index 664908e449a2bbaca932804cc67a89798707abda..8dd4ca29b63561d98508f0dedbcff765ebea2841 100644
--- a/chrome/browser/chromeos/drive/file_system.cc
+++ b/chrome/browser/chromeos/drive/file_system.cc
@@ -32,6 +32,7 @@
 #include "chrome/browser/chromeos/drive/search_metadata.h"
 #include "chrome/browser/chromeos/drive/sync_client.h"
 #include "chrome/common/pref_names.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/browser_thread.h"
 #include "google_apis/drive/drive_api_parser.h"
 
@@ -961,7 +962,7 @@ void FileSystem::MarkCacheFileAsUnmounted(
 }
 
 void FileSystem::AddPermission(const base::FilePath& drive_file_path,
-                               const std::string& email,
+                               const user_manager::UserID& user_id,
                                google_apis::drive::PermissionRole role,
                                const FileOperationCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
@@ -978,14 +979,14 @@ void FileSystem::AddPermission(const base::FilePath& drive_file_path,
                  entry),
       base::Bind(&FileSystem::AddPermissionAfterGetResourceEntry,
                  weak_ptr_factory_.GetWeakPtr(),
-                 email,
+                 user_id,
                  role,
                  callback,
                  base::Owned(entry)));
 }
 
 void FileSystem::AddPermissionAfterGetResourceEntry(
-    const std::string& email,
+    const user_manager::UserID& user_id,
     google_apis::drive::PermissionRole role,
     const FileOperationCallback& callback,
     ResourceEntry* entry,
@@ -999,7 +1000,7 @@ void FileSystem::AddPermissionAfterGetResourceEntry(
 
   scheduler_->AddPermission(
       entry->resource_id(),
-      email,
+      user_id,
       role,
       base::Bind(&RunFileOperationCallbackAsEntryActionCallback, callback));
 }