added the possibility to register a logger for internal services

doc/services.rst

@@ -215,6 +215,10 @@ don't want to mess with most of them.
   does not return a Response. Disable it with
   `unset($app['exception_handler'])`.
 
+* **logger**: A
+  `http://api.symfony.com/master/Symfony/Component/HttpKernel/Log/LoggerInterface.html`_
+  instance. By default, logging is disabled as the value is set to `null`.
+
 .. note::
 
     All of these Silex core services are shared.

src/Silex/Application.php

@@ -55,6 +55,8 @@ class Application extends \Pimple implements HttpKernelInterface, EventSubscribe
     {
         $app = $this;
 
+        $this['logger'] = null;
+
         $this['routes'] = $this->share(function () {
             return new RouteCollection();
         });
@@ -74,13 +76,13 @@ class Application extends \Pimple implements HttpKernelInterface, EventSubscribe
             $urlMatcher = new LazyUrlMatcher(function () use ($app) {
                 return $app['url_matcher'];
             });
-            $dispatcher->addSubscriber(new RouterListener($urlMatcher));
+            $dispatcher->addSubscriber(new RouterListener($urlMatcher, $app['logger']));
 
             return $dispatcher;
         });
 
         $this['resolver'] = $this->share(function () use ($app) {
-            return new ControllerResolver($app);
+            return new ControllerResolver($app, $app['logger']);
         });
 
         $this['kernel'] = $this->share(function () use ($app) {