diff -u b/core/includes/common.inc b/core/includes/common.inc
--- b/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -33,7 +33,7 @@
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Session\AnonymousUserSession;
-use Drupal\Core\Template\TemplateAttachmentManager;
+use Drupal\Core\Template\AttachmentManager;
 
 /**
  * @defgroup php_wrappers PHP wrapper functions
@@ -1672,9 +1672,9 @@
   );
 
   // Check for attachments added from a template.
-  if ($template_attachments = TemplateAttachmentManager::getAttachments('library')) {
+  if ($template_attachments = AttachmentManager::getAttachments('library')) {
     $elements['#attached']['library'] = array_merge($elements['#attached']['library'], $template_attachments);
-    TemplateAttachmentManager::clearAttachments('library');
+    AttachmentManager::clearAttachments('library');
   }
 
   // Add the libraries first.
reverted:
--- b/core/lib/Drupal/Core/Template/TemplateAttachmentManager.php
+++ /dev/null
@@ -1,54 +0,0 @@
-<?php
-/**
- * Contains \Drupal\Core\Template\TemplateAttachmentManager.
- */
-
-namespace Drupal\Core\Template;
-
-/**
- * Manages page attachments.
- */
-class TemplateAttachmentManager {
-
-  /**
-   * Stores page attachments.
-   *
-   * @var array
-   */
-  protected static $attachments;
-
-  /**
-   * Gets the page attachments.
-   *
-   * @param string $type
-   *   The attachment type.
-   *
-   * @return array
-   *   The page attachments.
-   */
-  public static function getAttachments($type = 'library') {
-    return isset(static::$attachments[$type]) ? static::$attachments[$type] : array();
-  }
-
-  /**
-   * Adds page attachments.
-   *
-   * @param mixed $attachments
-   *   An attachment name or an array of attachment names.
-   * @param string $type
-   *   The attachment type.
-   */
-  public static function addAttachments($attachments, $type = 'library') {
-    static::$attachments[$type][] = $attachments;
-  }
-
-  /**
-   * Clears page attachments.
-   *
-   * @param string $type
-   *   The attachment type.
-   */
-  public static function clearAttachments($type = 'library') {
-    static::$attachments[$type] = [];
-  }
-}
diff -u b/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
--- b/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -15,7 +15,7 @@
 use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\Core\Url;
 use Drupal\Core\Utility\LinkGeneratorInterface;
-use Drupal\Core\Template\TemplateAttachmentManager;
+use Drupal\Core\Template\AttachmentManager;
 
 /**
  * A class providing Drupal Twig extensions.
@@ -263,7 +263,7 @@
    *   An array of libraries.
    */
   public function addLibraries($libraries = array()) {
-    TemplateAttachmentManager::addAttachments($libraries, 'library');
+    AttachmentManager::addAttachments($libraries, 'library');
   }
 
 }
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/AttachmentManager.php
@@ -0,0 +1,57 @@
+<?php
+/**
+ * Contains \Drupal\Core\Template\AttachmentManager.
+ */
+
+namespace Drupal\Core\Template;
+
+/**
+ * Manages page attachments.
+ */
+class AttachmentManager {
+
+  /**
+   * Stores page attachments.
+   *
+   * @var array
+   */
+  protected static $attachments;
+
+  /**
+   * Gets the page attachments.
+   *
+   * @param string $type
+   *   The attachment type.
+   *
+   * @return array
+   *   The page attachments.
+   */
+  public static function getAttachments($type = 'library') {
+    return isset(static::$attachments[$type]) ? static::$attachments[$type] : array();
+  }
+
+  /**
+   * Adds page attachments.
+   *
+   * @param mixed $attachments
+   *   An array of attachment names or an attachment name.
+   * @param string $type
+   *   The attachment type.
+   */
+  public static function addAttachments($attachments, $type = 'library') {
+    if (!is_array(static::$attachments[$type])) {
+      static::clearAttachments($type);
+    }
+    static::$attachments[$type] = array_merge(static::$attachments[$type], (array) $attachments);
+  }
+
+  /**
+   * Clears page attachments.
+   *
+   * @param string $type
+   *   The attachment type.
+   */
+  public static function clearAttachments($type = 'library') {
+    static::$attachments[$type] = [];
+  }
+}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Template/AttachmentManagerTest.php
@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Template\AttachmentManagerTest.
+ */
+
+namespace Drupal\Tests\Core\Template;
+
+use Drupal\Core\Template\AttachmentManager;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Template\AttachmentManager
+ * @group Template
+ */
+class AttachmentManagerTest extends UnitTestCase {
+
+  /**
+   * Tests the static functions.
+   */
+  public function testStatics() {
+    $result = AttachmentManager::getAttachments();
+    $this->assertArrayEquals(array(), $result);
+    $attachments = array(
+      'special-css-library-1',
+      'special-js-library-1',
+    );
+    AttachmentManager::addAttachments($attachments);
+    $result = AttachmentManager::getAttachments();
+    $this->assertTrue(in_array($attachments[0], $result));
+    $this->assertTrue(in_array($attachments[1], $result));
+    $new_attachment = 'new-css-library';
+    AttachmentManager::addAttachments($new_attachment);
+    $result = AttachmentManager::getAttachments();
+    $this->assertTrue(in_array($new_attachment, $result));
+    $this->assertEquals(3, count($result));
+    AttachmentManager::clearAttachments();
+    $result = AttachmentManager::getAttachments();
+    $this->assertArrayEquals(array(), $result);
+  }
+
+}