core/includes/common.inc                           |  5 +-
 core/lib/Drupal/Core/Ajax/AjaxResponse.php         |  3 +-
 .../Ajax/CommandWithAttachedAssetsInterface.php    |  2 +-
 .../Core/Ajax/CommandWithAttachedAssetsTrait.php   |  3 +-
 core/lib/Drupal/Core/Asset/AttachedAssets.php      | 54 ----------------------
 core/lib/Drupal/Core/Render/Renderer.php           | 16 +++++++
 core/lib/Drupal/Core/Render/RendererInterface.php  | 44 ++++++++++++++++++
 7 files changed, 68 insertions(+), 59 deletions(-)

diff --git a/core/includes/common.inc b/core/includes/common.inc
index 2731dc1..654723c 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -33,6 +33,7 @@
 use Drupal\Core\Routing\GeneratorNotInitializedException;
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Renderer;
 use Drupal\Core\Session\AnonymousUserSession;
 
 /**
@@ -892,10 +893,10 @@ function drupal_js_defaults($data = NULL) {
  *   The merged #attached array.
  *
  * @deprecated To be removed in Drupal 8.0.x. Use
- *   \Drupal\Core\Asset\AttachedAssets::mergeAttachments() instead.
+ *   \Drupal\Core\Render\Renderer::mergeAttachments() instead.
  */
 function drupal_merge_attached(array $a, array $b) {
-  return AttachedAssets::mergeAttachments($a, $b);
+  return Renderer::mergeAttachments($a, $b);
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Ajax/AjaxResponse.php b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
index 766026d..91ceeb4 100644
--- a/core/lib/Drupal/Core/Ajax/AjaxResponse.php
+++ b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
@@ -8,6 +8,7 @@
 namespace Drupal\Core\Ajax;
 
 use Drupal\Core\Asset\AttachedAssets;
+use Drupal\Core\Render\Renderer;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
@@ -77,7 +78,7 @@ public function addCommand(CommandInterface $command, $prepend = FALSE) {
         'library' => $assets->getLibraries(),
         'drupalSettings' => $assets->getSettings(),
       ];
-      $attachments = AttachedAssets::mergeAttachments($this->attachments, $attachments);
+      $attachments = Renderer::mergeAttachments($this->attachments, $attachments);
       $this->setAttachments($attachments);
     }
 
diff --git a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsInterface.php b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsInterface.php
index 5ba1fa2..f55ce6c 100644
--- a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsInterface.php
+++ b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsInterface.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\Core\Ajax\CommandWithAttachedAssetsInterface.
+ * Contains \Drupal\Core\Ajax\CommandWithAttachedAssetsInterface.
  */
 
 namespace Drupal\Core\Ajax;
diff --git a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
index c8e3b83..e3f31b9 100644
--- a/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
+++ b/core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\Core\Ajax\CommandWithAttachedAssetsTrait.
+ * Contains \Drupal\Core\Ajax\CommandWithAttachedAssetsTrait.
  */
 
 namespace Drupal\Core\Ajax;
@@ -53,4 +53,5 @@ protected function getRenderedContent() {
   public function getAttachedAssets() {
     return $this->attachedAssets;
   }
+
 }
diff --git a/core/lib/Drupal/Core/Asset/AttachedAssets.php b/core/lib/Drupal/Core/Asset/AttachedAssets.php
index f0ef5ec..d94618e 100644
--- a/core/lib/Drupal/Core/Asset/AttachedAssets.php
+++ b/core/lib/Drupal/Core/Asset/AttachedAssets.php
@@ -5,7 +5,6 @@
  */
 
 namespace Drupal\Core\Asset;
-use Drupal\Component\Utility\NestedArray;
 
 /**
  * The default attached assets collection.
@@ -52,59 +51,6 @@ public static function createFromRenderArray(array $render_array) {
   }
 
   /**
-   * Merges two #attached arrays.
-   *
-   * The values under the 'drupalSettings' key are merged in a special way, to
-   * match the behavior of
-   *
-   * @code
-   *   jQuery.extend(true, {}, $settings_items[0], $settings_items[1], ...)
-   * @endcode
-   *
-   * This means integer indices are preserved just like string indices are,
-   * rather than re-indexed as is common in PHP array merging.
-   *
-   * Example:
-   * @code
-   * function module1_page_attachments(&$page) {
-   *   $page['a']['#attached']['drupalSettings']['foo'] = ['a', 'b', 'c'];
-   * }
-   * function module2_page_attachments(&$page) {
-   *   $page['#attached']['drupalSettings']['foo'] = ['d'];
-   * }
-   * // When the page is rendered after the above code, and the browser runs the
-   * // resulting <SCRIPT> tags, the value of drupalSettings.foo is
-   * // ['d', 'b', 'c'], not ['a', 'b', 'c', 'd'].
-   * @endcode
-   *
-   * By following jQuery.extend() merge logic rather than common PHP array merge
-   * logic, the following are ensured:
-   * - Attaching JavaScript settings is idempotent: attaching the same settings
-   *   twice does not change the output sent to the browser.
-   * - If pieces of the page are rendered in separate PHP requests and the
-   *   returned settings are merged by JavaScript, the resulting settings are
-   *   the same as if rendered in one PHP request and merged by PHP.
-   *
-   * @param array $a
-   *   An #attached array.
-   * @param array $b
-   *   Another #attached array.
-   *
-   * @return array
-   *   The merged #attached array.
-   */
-  public static function mergeAttachments(array $a, array $b) {
-    // If both #attached arrays contain drupalSettings, then merge them
-    // correctly; adding the same settings multiple times needs to behave
-    // idempotently.
-    if (!empty($a['drupalSettings']) && !empty($b['drupalSettings'])) {
-      $a['drupalSettings'] = NestedArray::mergeDeepArray([$a['drupalSettings'], $b['drupalSettings']], TRUE);
-      unset($b['drupalSettings']);
-    }
-    return NestedArray::mergeDeep($a, $b);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function setLibraries(array $libraries) {
diff --git a/core/lib/Drupal/Core/Render/Renderer.php b/core/lib/Drupal/Core/Render/Renderer.php
index 357ee6a..a3dd23d 100644
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Render;
 
+use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheContexts;
 use Drupal\Core\Cache\CacheFactoryInterface;
@@ -582,4 +583,19 @@ public static function mergeBubbleableMetadata(array $a, array $b) {
     return $a;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+
+  public static function mergeAttachments(array $a, array $b) {
+    // If both #attached arrays contain drupalSettings, then merge them
+    // correctly; adding the same settings multiple times needs to behave
+    // idempotently.
+    if (!empty($a['drupalSettings']) && !empty($b['drupalSettings'])) {
+      $a['drupalSettings'] = NestedArray::mergeDeepArray([$a['drupalSettings'], $b['drupalSettings']], TRUE);
+      unset($b['drupalSettings']);
+    }
+    return NestedArray::mergeDeep($a, $b);
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Render/RendererInterface.php b/core/lib/Drupal/Core/Render/RendererInterface.php
index 3625e66..990a087 100644
--- a/core/lib/Drupal/Core/Render/RendererInterface.php
+++ b/core/lib/Drupal/Core/Render/RendererInterface.php
@@ -304,4 +304,48 @@ public function getCacheableRenderArray(array $elements);
    */
   public static function mergeBubbleableMetadata(array $a, array $b);
 
+  /**
+   * Merges two attachments (#attached) arrays.
+   *
+   * The values under the 'drupalSettings' key are merged in a special way, to
+   * match the behavior of
+   *
+   * @code
+   *   jQuery.extend(true, {}, $settings_items[0], $settings_items[1], ...)
+   * @endcode
+   *
+   * This means integer indices are preserved just like string indices are,
+   * rather than re-indexed as is common in PHP array merging.
+   *
+   * Example:
+   * @code
+   * function module1_page_attachments(&$page) {
+   *   $page['a']['#attached']['drupalSettings']['foo'] = ['a', 'b', 'c'];
+   * }
+   * function module2_page_attachments(&$page) {
+   *   $page['#attached']['drupalSettings']['foo'] = ['d'];
+   * }
+   * // When the page is rendered after the above code, and the browser runs the
+   * // resulting <SCRIPT> tags, the value of drupalSettings.foo is
+   * // ['d', 'b', 'c'], not ['a', 'b', 'c', 'd'].
+   * @endcode
+   *
+   * By following jQuery.extend() merge logic rather than common PHP array merge
+   * logic, the following are ensured:
+   * - Attaching JavaScript settings is idempotent: attaching the same settings
+   *   twice does not change the output sent to the browser.
+   * - If pieces of the page are rendered in separate PHP requests and the
+   *   returned settings are merged by JavaScript, the resulting settings are
+   *   the same as if rendered in one PHP request and merged by PHP.
+   *
+   * @param array $a
+   *   An attachments (#attached) array.
+   * @param array $b
+   *   Another attachments (#attached) array.
+   *
+   * @return array
+   *   The merged attachments (#attached) array.
+   */
+  public static function mergeAttachments(array $a, array $b);
+
 }