Force encryption migration if the device supports ARC.

chrome/browser/chromeos/login/existing_user_controller.h

Index: chrome/browser/chromeos/login/existing_user_controller.h
diff --git a/chrome/browser/chromeos/login/existing_user_controller.h b/chrome/browser/chromeos/login/existing_user_controller.h
index bf392b33db3956e56a2cb8b055079a304f2ffb98..2ffc64adb3b5d674dda9bee513ed802c93b83ba8 100644
--- a/chrome/browser/chromeos/login/existing_user_controller.h
+++ b/chrome/browser/chromeos/login/existing_user_controller.h
@@ -220,6 +220,10 @@ class ExistingUserController
   void PerformLogin(const UserContext& user_context,
                     LoginPerformer::AuthorizationMode auth_mode);
 
+  // calls login() on previously-used |login_performer|.
+  void ContinuePerformLogin(const UserContext& user_context,
+                            LoginPerformer::AuthorizationMode auth_mode);

[xiyuan, 2017/04/06 16:08:59]

nit: maybe we should swap the order of args so that we can bind |auth_mode| on
creating the callback and avoid having to include login_performer.h.

i.e.

void ContinuePerformLogin(LoginPerformer::AuthorizationMode auth_mode,
                          const UserContext& user_context);

And bind the auth mode when creating the callback

base::BindOnce(&ExistingUserController::ContinuePerformLogin,
               weak_factory_.GetWeakPtr(),
               login_performer_->auth_mode());

And callback only needs a UserContext to be invoked.

[fukino, 2017/04/07 02:05:49]

Done.

+
   // Updates the |login_display_| attached to this controller.
   void UpdateLoginDisplay(const user_manager::UserList& users);