reverted:
--- b/core/includes/bootstrap.inc
+++ a/core/includes/bootstrap.inc
@@ -137,6 +137,47 @@
 define('DRUPAL_ROOT', dirname(dirname(__DIR__)));
 
 /**
+ * Returns the appropriate configuration directory.
+ *
+ * @param bool $require_settings
+ *   Only configuration directories with an existing settings.php file
+ *   will be recognized. Defaults to TRUE. During initial installation,
+ *   this is set to FALSE so that Drupal can detect a matching directory,
+ *   then create a new settings.php file in it.
+ * @param bool $reset
+ *   Force a full search for matching directories even if one had been
+ *   found previously. Defaults to FALSE.
+ * @param \Symfony\Component\HttpFoundation\Request $request
+ *   (optional) The current request. Defaults to \Drupal::request() or a new
+ *   request created from globals.
+ *
+ * @return string
+ *   The path of the matching directory.@see default.settings.php
+ *
+ * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
+ *   Use \Drupal\Core\DrupalKernel::getSitePath() instead. If the kernel is
+ *   unavailable or the site path needs to be recalculated then
+ *   Drupal\Core\DrupalKernel::findSitePath() can be used.
+ */
+function conf_path($require_settings = TRUE, $reset = FALSE, Request $request = NULL) {
+  if (!isset($request)) {
+    if (\Drupal::hasRequest()) {
+      $request = \Drupal::request();
+    }
+    // @todo Remove once external CLI scripts (Drush) are updated.
+    else {
+      $request = Request::createFromGlobals();
+    }
+  }
+  if (\Drupal::hasService('kernel')) {
+    $site_path = \Drupal::service('kernel')->getSitePath();
+  }
+  if (!isset($site_path) || empty($site_path)) {
+    $site_path = DrupalKernel::findSitePath($request, $require_settings);
+  }
+  return $site_path;
+}
+/**
  * Returns the path of a configuration directory.
  *
  * @param string $type
reverted:
--- b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
+++ a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
@@ -153,7 +153,7 @@
     }
 
     // Search the site-specific directory.
+    $searchdirs[static::ORIGIN_SITE] = conf_path();
-    $searchdirs[static::ORIGIN_SITE] = \Drupal::service('kernel')->getSitePath();
 
     // Unless an explicit value has been passed, manually check whether we are
     // in a test environment, in which case test extensions must be included.
diff -u b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
@@ -63,7 +63,13 @@
    *   The base path for public:// typically sites/default/files.
    */
   public static function basePath() {
-    $base_path = Settings::get('file_public_path', DrupalKernel::findSitePath(Request::createFromGlobals()) . '/files');
+    if (\Drupal::hasService('kernel')) {
+      $site_path = $site_path = \Drupal::service('kernel')->getSitePath();
+    }
+    else {
+      $site_path = DrupalKernel::findSitePath(Request::createFromGlobals());
+    }
+    $base_path = Settings::get('file_public_path', $site_path . '/files');
     return $base_path;
   }