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

vendor/symfony/dependency-injection/Tests/Fixtures/includes/ProjectWithXsdExtension.php

@@ -0,0 +1,19 @@
+<?php
+
+class ProjectWithXsdExtension extends ProjectExtension
+{
+    public function getXsdValidationBasePath()
+    {
+        return __DIR__.'/schema';
+    }
+
+    public function getNamespace()
+    {
+        return 'http://www.example.com/schema/projectwithxsd';
+    }
+
+    public function getAlias()
+    {
+        return 'projectwithxsd';
+    }
+}