[HttpKernel] Avoid updating the context if the request did not change

Due to the BC $this->setRequest() call in the onKernelRequest method, the
request is set twice every time in Symfony, and RequestContext::fromRequest
takes 1ms to run here so if we can skip one call it is a win.

src/Symfony/Component/HttpKernel/EventListener/RouterListener.php

@@ -35,6 +35,7 @@ class RouterListener implements EventSubscriberInterface
     private $matcher;
     private $context;
     private $logger;
+    private $request;
 
     /**
      * Constructor.
@@ -72,9 +73,10 @@ public function __construct($matcher, RequestContext $context = null, LoggerInte
      */
     public function setRequest(Request $request = null)
     {
-        if (null !== $request) {
+        if (null !== $request && $this->request !== $request) {
             $this->context->fromRequest($request);
         }
+        $this->request = $request;
     }
 
     public function onKernelRequest(GetResponseEvent $event)