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

vendor/symfony/http-kernel/DataCollector/DataCollector.php

@@ -0,0 +1,58 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpKernel\DataCollector;
+
+use Symfony\Component\HttpKernel\DataCollector\Util\ValueExporter;
+
+/**
+ * DataCollector.
+ *
+ * Children of this class must store the collected data in the data property.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ * @author Bernhard Schussek <bschussek@symfony.com>
+ */
+abstract class DataCollector implements DataCollectorInterface, \Serializable
+{
+    protected $data = array();
+
+    /**
+     * @var ValueExporter
+     */
+    private $valueExporter;
+
+    public function serialize()
+    {
+        return serialize($this->data);
+    }
+
+    public function unserialize($data)
+    {
+        $this->data = unserialize($data);
+    }
+
+    /**
+     * Converts a PHP variable to a string.
+     *
+     * @param mixed $var A PHP variable
+     *
+     * @return string The string representation of the variable
+     */
+    protected function varToString($var)
+    {
+        if (null === $this->valueExporter) {
+            $this->valueExporter = new ValueExporter();
+        }
+
+        return $this->valueExporter->exportValue($var);
+    }
+}