Merge branch '3.2'

* 3.2:
  [2.7] Fix issues reported by static analyse
  [Serializer] Reduce nesting in YamlFileLoader
  [DependencyInjection] add missing dumped private services list in a container frozen constructor.

Author: nicolas-grekas

EventListener/AbstractTestSessionListener.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\HttpKernel\EventListener;
 
 use Symfony\Component\HttpFoundation\Cookie;
+use Symfony\Component\HttpFoundation\Session\SessionInterface;
 use Symfony\Component\HttpKernel\KernelEvents;
 use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
 use Symfony\Component\HttpKernel\Event\GetResponseEvent;