Update to drupal-org-drupal 8.0.0-rc2. For more information, see https://www.drupal.org/node/2598668

core/modules/config_translation/src/ConfigMapperInterface.php

@@ -9,7 +9,6 @@ namespace Drupal\config_translation;
 
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
-use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\RouteCollection;
 
 /**
@@ -175,6 +174,9 @@ interface ConfigMapperInterface {
   /**
    * Adds the given configuration name to the list of names.
    *
+   * Note that it is the responsibility of the calling code to ensure that the
+   * configuration exists.
+   *
    * @param string $name
    *   Configuration name.
    */