Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/dependency-injection/Tests/Fixtures/containers/container16.php

@@ -0,0 +1,11 @@
+<?php
+
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+$container = new ContainerBuilder();
+$container
+    ->register('foo', 'FooClass\\Foo')
+    ->setDecoratedService('bar')
+;
+
+return $container;