Update to Drupal 8.1.1. For more information, see https://www.drupal.org/node/2718713

core/lib/Drupal/Core/Cache/Context/PathParentCacheContext.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Drupal\Core\Cache\Context;
+
+use Drupal\Core\Cache\CacheableMetadata;
+
+/**
+ * Defines a cache context service for path parents.
+ *
+ * Cache context ID: 'url.path.parent'.
+ *
+ * This allows for caching based on the path, excluding everything after the
+ * last forward slash.
+ */
+class PathParentCacheContext extends RequestStackCacheContextBase implements CacheContextInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel() {
+    return t('Parent path');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext() {
+    $request = $this->requestStack->getCurrentRequest();
+    $path_elements = explode('/', trim($request->getPathInfo(), '/'));
+    array_pop($path_elements);
+    return implode('/', $path_elements);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata() {
+    return new CacheableMetadata();
+  }
+
+}