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

vendor/phpunit/php-code-coverage/src/CodeCoverage/Driver/HHVM.php

@@ -0,0 +1,26 @@
+<?php
+/*
+ * This file is part of the PHP_CodeCoverage package.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/**
+ * Driver for HHVM's code coverage functionality.
+ *
+ * @since Class available since Release 2.2.2
+ * @codeCoverageIgnore
+ */
+class PHP_CodeCoverage_Driver_HHVM extends PHP_CodeCoverage_Driver_Xdebug
+{
+    /**
+     * Start collection of code coverage information.
+     */
+    public function start()
+    {
+        xdebug_start_code_coverage();
+    }
+}