reverted:
--- b/core/core.services.yml
+++ a/core/core.services.yml
@@ -1219,7 +1219,8 @@
     tags:
       - { name: twig.extension, priority: 100 }
     calls:
+      - [setGenerators, ['@url_generator']]
+      - [setLinkGenerator, ['@link_generator']]
-      - [setDependencies, ['@url_generator', '@link_generator', '@theme.manager']]
   # @todo Figure out what to do about debugging functions.
   # @see http://drupal.org/node/1804998
   twig.extension.debug:
reverted:
--- b/core/lib/Drupal/Core/Template/TwigExtension.php
+++ a/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -15,7 +15,6 @@
 use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\Core\Url;
 use Drupal\Core\Utility\LinkGeneratorInterface;
-use Drupal\Core\Theme\ThemeManagerInterface;
 
 /**
  * A class providing Drupal Twig extensions.
@@ -41,28 +40,26 @@
   protected $linkGenerator;
 
   /**
+   * Constructs \Drupal\Core\Template\TwigExtension.
-   * The theme manager.
    *
+   * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
+   *   The URL generator.
-   * @var \Drupal\Core\Theme\ThemeManagerInterface;
    */
+  public function setGenerators(UrlGeneratorInterface $url_generator) {
+    $this->urlGenerator = $url_generator;
+    return $this;
+  }
-  protected $themeManager;
 
   /**
+   * Sets the link generator.
-   * Constructs \Drupal\Core\Template\TwigExtension.
    *
-   * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
-   *   The URL generator.
    * @param \Drupal\Core\Utility\LinkGeneratorInterface $link_generator
    *   The link generator.
-   * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
-   *   The theme manager.
    *
    * @return $this
    */
+  public function setLinkGenerator(LinkGeneratorInterface $link_generator) {
-  public function setDependencies(UrlGeneratorInterface $url_generator, LinkGeneratorInterface $link_generator, ThemeManagerInterface $theme_manager) {
-    $this->urlGenerator = $url_generator;
     $this->linkGenerator = $link_generator;
-    $this->themeManager = $theme_manager;
     return $this;
   }
 
@@ -80,7 +77,6 @@
       new \Twig_SimpleFunction('url_from_path', array($this, 'getUrlFromPath'), array('is_safe_callback' => array($this, 'isUrlGenerationSafe'))),
       new \Twig_SimpleFunction('link', array($this, 'getLink')),
       new \Twig_SimpleFunction('file_url', 'file_create_url'),
-      new \Twig_SimpleFunction('active_theme', array($this, 'activeTheme')),
     );
   }
 
@@ -223,16 +219,6 @@
   }
 
   /**
-   * Gets the name of the active theme.
-   *
-   * @return string
-   *   The name of the active theme.
-   */
-  public function activeTheme() {
-    return $this->themeManager->getActiveTheme()->getName();
-  }
-
-  /**
    * Determines at compile time whether the generated URL will be safe.
    *
    * Saves the unneeded automatic escaping for performance reasons.
reverted:
--- b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
+++ a/core/modules/system/src/Tests/Theme/EngineTwigTest.php
@@ -111,13 +111,4 @@
     $this->assertRaw('<div>file_url: ' . $filepath . '</div>');
   }
 
-  /**
-   * Tests the active_theme() function.
-   */
-  public function testActiveTheme() {
-    $this->drupalGet('/twig-theme-test/active_theme');
-    $theme = \Drupal::service('theme.manager')->getActiveTheme()->getName();
-    $this->assertRaw('<div>active theme: ' . $theme . '</div>');
-  }
-
 }
reverted:
--- b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -75,11 +75,4 @@
     return array('#theme' => 'twig_registry_loader_test');
   }
 
-  /**
-   * Menu callback for testing the active theme function.
-   */
-  public function activeThemeRender() {
-    return array('#theme' => 'twig_theme_test_active_theme');
-  }
-
 }
reverted:
--- b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.active_theme.html.twig
+++ /dev/null
@@ -1 +0,0 @@
-<div>active theme: {{ active_theme() }}</div>
reverted:
--- b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -50,10 +50,6 @@
     'variables' => array(),
     'template' => 'twig_theme_test.file_url',
   );
-  $items['twig_theme_test_active_theme'] = array(
-    'variables' => array(),
-    'template' => 'twig_theme_test.active_theme',
-  );
   return $items;
 }
 
reverted:
--- b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
+++ a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
@@ -46,10 +46,3 @@
     _controller: '\Drupal\twig_theme_test\TwigThemeTestController::registryLoaderRender'
   requirements:
     _access: 'TRUE'
-
-twig_theme_test_active_theme:
-  path: '/twig-theme-test/active_theme'
-  defaults:
-    _controller: '\Drupal\twig_theme_test\TwigThemeTestController::activeThemeRender'
-  requirements:
-    _access: 'TRUE'
reverted:
--- b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -31,13 +31,7 @@
       'autoescape' => TRUE,
       'optimizations' => 0
     ));
+    $twig->addExtension((new TwigExtension())->setGenerators($this->getMock('Drupal\Core\Routing\UrlGeneratorInterface')));
-    $twig->addExtension((new TwigExtension())
-      ->setDependencies(
-        $this->getMock('Drupal\Core\Routing\UrlGeneratorInterface'),
-        $this->getMock('Drupal\Core\Utility\LinkGeneratorInterface'),
-        $this->getMock('Drupal\Core\Theme\ThemeManagerInterface')
-      )
-    );
 
     $nodes = $twig->parse($twig->tokenize($template));