diff --git a/core/includes/common.inc b/core/includes/common.inc
index 225028a..c5e1d9d 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -871,14 +871,15 @@ function drupal_set_time_limit($time_limit) {
  * This function should only be used when including a file containing PHP code;
  * the 'module://', 'profile://' and 'theme://' stream wrappers should be used
  * for other use cases.
- * @param $type
+ *
+ * @param string $type
  *   The type of the item; one of 'core', 'profile', 'module', 'theme', or
  *   'theme_engine'.
- * @param $name
+ * @param string $name
  *   The name of the item for which the path is requested. Ignored for
  *   $type 'core'.
  *
- * @return
+ * @return string
  *   The path to the requested item or an empty string if the item is not found.
  */
 function drupal_get_path($type, $name) {
diff --git a/core/lib/Drupal/Core/StreamWrapper/LocalStream.php b/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
index fbec988..01c3186 100644
--- a/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/LocalStream.php
@@ -125,11 +125,11 @@ protected function getLocalPath($uri = NULL) {
     if (!isset($uri)) {
       $uri = $this->uri;
     }
-    $path = $this->getDirectoryPath() . '/' . $this->getTarget($uri);
+    $path = $this->getDirectoryPath() . DIRECTORY_SEPARATOR . $this->getTarget($uri);
     $realpath = realpath($path);
     if (!$realpath) {
       // This file does not yet exist.
-      $realpath = realpath(dirname($path)) . '/' . drupal_basename($path);
+      $realpath = realpath(dirname($path)) . DIRECTORY_SEPARATOR . drupal_basename($path);
     }
     $directory = realpath($this->getDirectoryPath());
     if (!$realpath || !$directory || strpos($realpath, $directory) !== 0) {
@@ -426,7 +426,7 @@ public function mkdir($uri, $mode, $options) {
     if ($recursive) {
       // $this->getLocalPath() fails if $uri has multiple levels of directories
       // that do not yet exist.
-      $localpath = $this->getDirectoryPath() . '/' . $this->getTarget($uri);
+      $localpath = $this->getDirectoryPath() . DIRECTORY_SEPARATOR . $this->getTarget($uri);
     }
     else {
       $localpath = $this->getLocalPath($uri);
diff --git a/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
index a3df6e3..4e2f420 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
@@ -17,7 +17,7 @@ class ModuleStream extends SystemStream {
    */
   protected function getOwnerName() {
     $name = parent::getOwnerName();
-    if (\Drupal::moduleHandler()->moduleExists($name)) {
+    if ($this->moduleHandler()->moduleExists($name)) {
       return $name;
     }
     else {
@@ -27,12 +27,16 @@ protected function getOwnerName() {
   }
 
   /**
-   * Gets the module's directory path.
-   *
-   * @return string
-   *   String specifying the path.
+   * {@inheritdoc}
    */
   protected function getDirectoryPath() {
     return drupal_get_path('module', $this->getOwnerName());
   }
+
+  /**
+   * Wraps the ModuleHandler service.
+   */
+  protected function moduleHandler() {
+    return \Drupal::moduleHandler();
+  }
 }
diff --git a/core/lib/Drupal/Core/StreamWrapper/ProfileStream.php b/core/lib/Drupal/Core/StreamWrapper/ProfileStream.php
index eff73ed..e36ede2 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ProfileStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ProfileStream.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\StreamWrapper;
 
 /**
- * Defines the read-only profile:// stream wrapper for profiles.
+ * Defines the read-only profile:// stream wrapper for profile files.
  */
 class ProfileStream extends SystemStream {
 
@@ -31,10 +31,7 @@ protected function getOwnerName() {
   }
 
   /**
-   * Gets the profile's directory path.
-   *
-   * @return string
-   *   String specifying the path.
+   * {@inheritdoc}
    */
   protected function getDirectoryPath() {
     return drupal_get_path('profile', $this->getOwnerName());
diff --git a/core/lib/Drupal/Core/StreamWrapper/SystemStream.php b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
index c337400..728bb67 100644
--- a/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
@@ -7,18 +7,21 @@
 
 namespace Drupal\Core\StreamWrapper;
 
-use \Drupal\Component\Utility\UrlHelper;
-
 /**
  * Defines a base stream wrapper implementation.
  *
- * This class provides a read-only Drupal stream wrapper base class for system
- * files such as modules, themes and profiles.
+ * SystemStream is a read-only Drupal stream wrapper base class for system files
+ * located in modules, themes and profiles.
  */
 abstract class SystemStream extends LocalReadOnlyStream {
 
   /**
-   * Get the module, theme, or profile name of the current URI.
+   * Gets the module, theme, or profile name of the current URI.
+   *
+   * This will return the name of the module, theme or profile e.g.
+   * @code SystemStream::getOwnerName('module://foo') @endcode and @code
+   * SystemStream::getOwnerName('module://foo/')@endcode will both return @code
+   * 'foo'@endcode
    *
    * @return string
    *   The extension name.
@@ -45,18 +48,7 @@ protected function getTarget($uri = NULL) {
   }
 
   /**
-   * Returns a web accessible URL for the resource.
-   *
-   * This function should return a URL that can be embedded in a web page
-   * and accessed from a browser. For example, the external URL of
-   * "youtube://xIpLd0WQKCY" might be
-   * "http://www.youtube.com/watch?v=xIpLd0WQKCY".
-   *
-   * @param string $uri
-   *   An optional URI.
-   *
-   * @return string
-   *   Returns a string containing a web accessible URL for the resource.
+   * {@inheritdoc}
    *
    * @throws \InvalidArgumentException
    */
@@ -65,7 +57,7 @@ public function getExternalUrl() {
     if (empty($dir)) {
       throw new \InvalidArgumentException(sprintf('Extension directory for %s does not exist.', $this->uri));
     }
-    return \Drupal::request()->getUriForPath(base_path() . $dir . $this->getTarget());
+    return $this->request()->getUriForPath(base_path() . $dir . $this->getTarget());
   }
 
   /**
@@ -79,11 +71,18 @@ public function dirname($uri = NULL) {
     $target = $this->getTarget($uri);
     $dirname = dirname($target);
 
-    if ($dirname == '.') {
+    if ($dirname === '.' || $dirname === '\\') {
       $dirname = '';
     }
 
     return rtrim($scheme . '://' . $this->getOwnerName() . $dirname, '/');
   }
 
+  /**
+   * Wraps the drupal request.
+   */
+  protected function request() {
+    return \Drupal::request();
+  }
+
 }
diff --git a/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
index c6c4c48..31ff89e 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
@@ -25,7 +25,7 @@ protected function getOwnerName() {
         $name = $this->themeHandler()->getDefault();
         break;
       case 'admin':
-        $name = \Drupal::config('system.theme')->get('admin');
+        $name = $this->config('system.theme')->get('admin');
         break;
     }
     // Return name only for installed themes.
@@ -39,10 +39,7 @@ protected function getOwnerName() {
   }
 
   /**
-   * Gets the theme's directory path.
-   *
-   * @return string
-   *   String specifying the path.
+   * {@inheritdoc}
    */
   protected function getDirectoryPath() {
     return drupal_get_path('theme', $this->getOwnerName());
@@ -63,4 +60,11 @@ protected function getActiveTheme() {
   protected function themeHandler() {
     return \Drupal::service('theme_handler');
   }
+
+  /**
+   * Wraps the drupal configuration service.
+   */
+  protected function config($config_name) {
+    return \Drupal::config($config_name);
+  }
 }
diff --git a/core/modules/system/src/Tests/File/SystemStreamTest.php b/core/modules/system/src/Tests/File/SystemStreamTest.php
index b43b836..02b75ab 100644
--- a/core/modules/system/src/Tests/File/SystemStreamTest.php
+++ b/core/modules/system/src/Tests/File/SystemStreamTest.php
@@ -356,6 +356,11 @@ private function runTestOnInstanceMethod($instance, $method, array $data) {
         }
       }
       else {
+        if ($method == 'realpath') {
+          // realpath() returns strings with the OS-specific DIRECTORY_SEPARATOR,
+          // make sure we are testing for that.
+          $info[0] = str_replace('/', DIRECTORY_SEPARATOR, $info[0]);
+        }
         $this->assertEqual($instance->$method(), $info[0], $info[1]);
       }
     }