diff -u b/core/lib/Drupal/Core/ControllerResolver.php b/core/lib/Drupal/Core/ControllerResolver.php
--- b/core/lib/Drupal/Core/ControllerResolver.php
+++ b/core/lib/Drupal/Core/ControllerResolver.php
@@ -66,15 +66,14 @@
    *   If the controller class does not exist
    */
   protected function createController($controller) {
-    // service:method
+    // Controller in the service:method notation.
     $count = substr_count($controller, ':');
     if ($count == 1) {
-      // controller in the service:method notation
       list($service, $method) = explode(':', $controller, 2);
       return array($this->container->get($service), $method);
     }
 
-    // class::method
+    // Controller in the class::method notation.
     if (strpos($controller, '::') !== FALSE) {
       list($class, $method) = explode('::', $controller, 2);
       if (!class_exists($class)) {
@@ -99,2 +98,3 @@
   }
+
 }