Issue #2223593 by znerol: Decouple the router.request_context service from the request service.

core/core.services.yml

@@ -291,8 +291,8 @@ services:
     arguments: ['@database', '@lock']
   router.request_context:
     class: Symfony\Component\Routing\RequestContext
-    calls:
-      - [fromRequest, ['@request']]
+    tags:
+      - { name: persist }
   router.admin_context:
     class: Drupal\Core\Routing\AdminContext
     arguments: ['@request_stack']
@@ -467,7 +467,7 @@ services:
     class: Symfony\Component\HttpKernel\EventListener\RouterListener
     tags:
       - { name: event_subscriber }
-    arguments: ['@router']
+    arguments: ['@router', '@router.request_context', NULL, '@request_stack']
   content_negotiation:
     class: Drupal\Core\ContentNegotiation
   view_subscriber:

core/modules/simpletest/lib/Drupal/simpletest/TestBase.php

@@ -1160,6 +1160,12 @@ protected function rebuildContainer($environment = 'testing') {
       $this->container->get('request_stack')->push($request);
     }
     $this->container->get('current_user')->setAccount(\Drupal::currentUser());
+
+    // The request context is normally set by the router_listener from within
+    // its KernelEvents::REQUEST listener. In the simpletest parent site this
+    // event is not fired, therefore it is necessary to updated the request
+    // context manually here.
+    $this->container->get('router.request_context')->fromRequest($request);
   }
 
   /**