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

chrome/browser/drive/drive_api_service.h

Index: chrome/browser/drive/drive_api_service.h
diff --git a/chrome/browser/drive/drive_api_service.h b/chrome/browser/drive/drive_api_service.h
index 61a655009618a29a7d6250380a15a8fd47062664..10d85c3cc193331f9243432429fed93d8895039d 100644
--- a/chrome/browser/drive/drive_api_service.h
+++ b/chrome/browser/drive/drive_api_service.h
@@ -235,7 +235,7 @@ class DriveAPIService : public DriveServiceInterface,
       const google_apis::EntryActionCallback& callback) override;
   google_apis::CancelCallback AddPermission(
       const std::string& resource_id,
-      const std::string& email,
+      const user_manager::UserID& user_id,
       google_apis::drive::PermissionRole role,
       const google_apis::EntryActionCallback& callback) override;
   scoped_ptr<BatchRequestConfiguratorInterface> StartBatchRequest() override;