Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/toolbar/src/PageCache/AllowToolbarPath.php

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\toolbar\PageCache\AllowToolbarPath.
+ */
+
+namespace Drupal\toolbar\PageCache;
+
+use Drupal\Core\PageCache\RequestPolicyInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Cache policy for the toolbar page cache service.
+ *
+ * This policy allows caching of requests directed to /toolbar/subtrees/{hash}
+ * even for authenticated users.
+ */
+class AllowToolbarPath implements RequestPolicyInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function check(Request $request) {
+    // Note that this regular expression matches the end of pathinfo in order to
+    // support multilingual sites using path prefixes.
+    if (preg_match('#/toolbar/subtrees/[^/]+(/[^/]+)?$#', $request->getPathInfo())) {
+      return static::ALLOW;
+    }
+  }
+
+}