Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/lib/Drupal/Component/ClassFinder/ClassFinder.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Drupal\Component\ClassFinder;
+
+use Doctrine\Common\Reflection\ClassFinderInterface;
+
+/**
+ * A Utility class that uses active autoloaders to find a file for a class.
+ */
+class ClassFinder implements ClassFinderInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function findFile($class) {
+    $loaders = spl_autoload_functions();
+    foreach ($loaders as $loader) {
+      if (is_array($loader) && isset($loader[0]) && is_object($loader[0]) && method_exists($loader[0], 'findFile')) {
+        $file = call_user_func_array([$loader[0], 'findFile'], [$class]);
+        // Different implementations return different empty values. For example,
+        // \Composer\Autoload\ClassLoader::findFile() returns FALSE whilst
+        // \Doctrine\Common\Reflection\ClassFinderInterface::findFile()
+        // documents that a NULL should be returned.
+        if (!empty($file)) {
+          return $file;
+        }
+      }
+    }
+    return NULL;
+  }
+
+}