diff --git a/core/core.services.yml b/core/core.services.yml
index 66a46c6603..181ab27423 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -479,7 +479,7 @@ services:
     arguments: ['@app.root', '@module_handler', '@cache.discovery']
   theme.negotiator:
     class: Drupal\Core\Theme\ThemeNegotiator
-    arguments: ['@access_check.theme', '@class_resolver']
+    arguments: ['@access_check.theme', '@current_route_match']
     tags:
       - { name: service_id_collector, tag: theme_negotiator }
   theme.negotiator.default:
diff --git a/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php b/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php
new file mode 100644
index 0000000000..d5e87343e4
--- /dev/null
+++ b/core/lib/Drupal/Core/Theme/ChainThemeNegotiatorInterface.php
@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Theme\ChainThemeNegotiatorInterface.
+ */
+
+namespace Drupal\Core\Theme;
+
+/**
+ * Defines an interface for a chained service which determines the active theme.
+ */
+interface ChainThemeNegotiatorInterface extends ThemeNegotiatorInterface {
+
+  /**
+   * Adds a active theme negotiation service.
+   *
+   * @param \Drupal\Core\Theme\ThemeNegotiatorInterface $negotiator
+   *   The theme negotiator to add.
+   * @param int $priority
+   *   Priority of the theme negotiator.
+   */
+  public function addNegotiator(ThemeNegotiatorInterface $negotiator, $priority);
+
+  /**
+   * Determines the active theme.
+   *
+   * @return string|null
+   *   Returns the active theme name, else return NULL.
+   *
+   * @see \Drupal\Core\Theme\ThemeNegotiatorInterface::determineActiveTheme()
+   */
+  public function getActiveTheme();
+
+}
diff --git a/core/lib/Drupal/Core/Theme/ThemeNegotiator.php b/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
index 18b618cedb..77c6f291fb 100644
--- a/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
+++ b/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
@@ -11,14 +11,14 @@
  * It therefore uses ThemeNegotiatorInterface objects which are passed in
  * using the 'theme_negotiator' tag.
  */
-class ThemeNegotiator implements ThemeNegotiatorInterface {
+class ThemeNegotiator implements ChainThemeNegotiatorInterface {
 
   /**
    * Holds an array of theme negotiator IDs, sorted by priority.
    *
    * @var string[]
    */
-  protected $negotiators = [];
+  protected $negotiators = array();
 
   /**
    * The access checker for themes.
@@ -34,20 +34,53 @@ class ThemeNegotiator implements ThemeNegotiatorInterface {
    */
   protected $classResolver;
 
+  /**
+   * The current route match.
+   *
+   * @var \Drupal\Core\Routing\RouteMatchInterface
+   */
+  protected $routeMatch;
+
   /**
    * Constructs a new ThemeNegotiator.
    *
    * @param \Drupal\Core\Theme\ThemeAccessCheck $theme_access
    *   The access checker for themes.
-   * @param \Drupal\Core\DependencyInjection\ClassResolverInterface $class_resolver
-   *   The class resolver.
-   * @param string[] $negotiators
-   *   An array of negotiator IDs.
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The current route match.
    */
-  public function __construct(ThemeAccessCheck $theme_access, ClassResolverInterface $class_resolver, array $negotiators) {
+  public function __construct(ThemeAccessCheck $theme_access, RouteMatchInterface $route_match) {
     $this->themeAccess = $theme_access;
-    $this->negotiators = $negotiators;
-    $this->classResolver = $class_resolver;
+    $this->routeMatch = $route_match;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addNegotiator(ThemeNegotiatorInterface $negotiator, $priority) {
+    $this->negotiators[$priority][] = $negotiator;
+    // Force the negotiators to be re-sorted.
+    $this->sortedNegotiators = NULL;
+  }
+
+  /**
+   * Returns the sorted array of theme negotiators.
+   *
+   * @return array|\Drupal\Core\Theme\ThemeNegotiatorInterface[]
+   *   An array of theme negotiator objects.
+   */
+  protected function getSortedNegotiators() {
+    if (!isset($this->sortedNegotiators)) {
+      // Sort the negotiators according to priority.
+      krsort($this->negotiators);
+      // Merge nested negotiators from $this->negotiators into
+      // $this->sortedNegotiators.
+      $this->sortedNegotiators = array();
+      foreach ($this->negotiators as $builders) {
+        $this->sortedNegotiators = array_merge($this->sortedNegotiators, $builders);
+      }
+    }
+    return $this->sortedNegotiators;
   }
 
   /**
@@ -73,4 +106,11 @@ public function determineActiveTheme(RouteMatchInterface $route_match) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getActiveTheme() {
+    return $this->determineActiveTheme($this->routeMatch);
+  }
+
 }
diff --git a/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php b/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
index 1e2303d7c4..0a8d2fb50e 100644
--- a/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
@@ -44,13 +44,18 @@ class ThemeNegotiatorTest extends UnitTestCase {
   protected $themeNegotiator;
 
   /**
-   * {@inheritdoc}
+   * The current route match.
+   *
+   * @var \Drupal\Core\Routing\RouteMatchInterface
    */
+  protected $routeMatch;
+
   protected function setUp() {
     $this->themeAccessCheck = $this->getMockBuilder('\Drupal\Core\Theme\ThemeAccessCheck')
       ->disableOriginalConstructor()
       ->getMock();
-    $this->container = new ContainerBuilder();
+    $this->routeMatch = new RouteMatch('test_route', new Route('/test-route'), array(), array());
+    $this->themeNegotiator = new ThemeNegotiator($this->themeAccessCheck, $this->routeMatch);
   }
 
   /**
@@ -75,8 +80,7 @@ public function testDetermineActiveTheme() {
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
-    $route_match = new RouteMatch('test_route', new Route('/test-route'), [], []);
-    $theme = $this->createThemeNegotiator($negotiators)->determineActiveTheme($route_match);
+    $theme = $this->themeNegotiator->determineActiveTheme($this->routeMatch);
 
     $this->assertEquals('example_test', $theme);
   }
@@ -115,8 +119,7 @@ public function testDetermineActiveThemeWithPriority() {
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
-    $route_match = new RouteMatch('test_route', new Route('/test-route'), [], []);
-    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
+    $theme = $this->themeNegotiator->determineActiveTheme($this->routeMatch);
 
     $this->assertEquals('example_test', $theme);
   }
@@ -163,8 +166,7 @@ public function testDetermineActiveThemeWithAccessCheck() {
       ->with('example_test2')
       ->will($this->returnValue(TRUE));
 
-    $route_match = new RouteMatch('test_route', new Route('/test-route'), [], []);
-    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
+    $theme = $this->themeNegotiator->determineActiveTheme($this->routeMatch);
 
     $this->assertEquals('example_test2', $theme);
   }
@@ -204,8 +206,7 @@ public function testDetermineActiveThemeWithNotApplyingNegotiator() {
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
-    $route_match = new RouteMatch('test_route', new Route('/test-route'), [], []);
-    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
+    $theme = $this->themeNegotiator->determineActiveTheme($this->routeMatch);
 
     $this->assertEquals('example_test2', $theme);
   }