add back getRouteParameters()
START PART 2:  https://www.drupal.org/node/2301273
apply patch https://www.drupal.org/files/issues/menu-2256521-MenuLinkTree-review-do-not-test.patch
START PART 3: https://www.drupal.org/node/2301313
apply patch https://www.drupal.org/files/issues/menu-2256521-MenuLinkContentUI-review-do-not-test.patch