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

vendor/symfony/dependency-injection/Compiler/ExtensionCompilerPass.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace Symfony\Component\DependencyInjection\Compiler;
+
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+/**
+ * A pass to automatically process extensions if they implement 
+ * CompilerPassInterface.
+ *
+ * @author Wouter J <wouter@wouterj.nl>
+ */
+class ExtensionCompilerPass implements CompilerPassInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function process(ContainerBuilder $container)
+    {
+        foreach ($container->getExtensions() as $extension) {
+            if (!$extension instanceof CompilerPassInterface) {
+                continue;
+            }
+
+            $extension->process($container);
+        }
+    }
+}