core/includes/theme.inc                            | 19 ---------
 .../modules/system/src/MessagesPostRenderCache.php | 47 +++++++++++++++++++---
 .../src/Plugin/Block/SystemPageMessagesBlock.php   | 36 +++++------------
 core/modules/system/system.services.yml            |  1 +
 4 files changed, 52 insertions(+), 51 deletions(-)

diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index b51ea8e..b71c17f 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -523,25 +523,6 @@ function template_preprocess_datetime_wrapper(&$variables) {
 }
 
 /**
- * Prepares variables for status message templates.
- *
- * Default template: status-messages.html.twig.
- *
- * @param array $variables
- *   An associative array containing:
- *   - display: (optional) May have a value of 'status' or 'error' when only
- *     displaying messages of that specific type.
- */
-function template_preprocess_status_messages(&$variables) {
-  $variables['message_list'] = drupal_get_messages($variables['display']);
-  $variables['status_headings'] = array(
-    'status' => t('Status message'),
-    'error' => t('Error message'),
-    'warning' => t('Warning message'),
-  );
-}
-
-/**
  * Prepares variables for links templates.
  *
  * Default template: links.html.twig.
diff --git a/core/modules/system/src/MessagesPostRenderCache.php b/core/modules/system/src/MessagesPostRenderCache.php
index f25f67b..2cfc912 100644
--- a/core/modules/system/src/MessagesPostRenderCache.php
+++ b/core/modules/system/src/MessagesPostRenderCache.php
@@ -7,6 +7,9 @@
 
 namespace Drupal\system;
 
+use Drupal\Core\Render\Renderer;
+use Drupal\Core\Render\RendererInterface;
+
 /**
  * Defines a service for messages post render cache callbacks.
  */
@@ -14,10 +17,29 @@ class MessagesPostRenderCache {
 
   /**
    * The messages.
-   * They are stored in a static property so they can appear in multiple blocks.
    *
+   * They are stored in a property so they can appear in multiple blocks.
+   *
+   * @var string[]
+   */
+  protected $messages;
+
+  /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
    */
-  protected static $messages;
+  protected $renderer;
+
+  /**
+   * Constructs a new MessagesPostRenderCache object.
+   *
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer.
+   */
+  public function __construct(RendererInterface $renderer) {
+    $this->renderer = $renderer;
+  }
 
   /**
    * #post_render_cache callback; replaces placeholder with messages.
@@ -31,13 +53,28 @@ class MessagesPostRenderCache {
    *   A renderable array containing the messages.
    */
   public function renderMessages(array $element, array $context) {
-    if (!isset(static::$messages)) {
-      static::$messages = drupal_get_messages();
+    // Collect the messages.
+    if (!isset($this->messages)) {
+      $this->messages = drupal_get_messages();
     }
 
+    // Render the messages.
+    $messages = [
+      '#theme' => 'status_messages',
+      '#message_list' => $this->messages,
+      '#status_headings' => [
+        'status' => t('Status message'),
+        'error' => t('Error message'),
+        'warning' => t('Warning message'),
+      ],
+    ];
+    $markup = $this->renderer->render($messages);
+
+    // Replace the placeholder.
     $callback = 'system.messages_post_render_cache:renderMessages';
     $placeholder = drupal_render_cache_generate_placeholder($callback, $context);
-    $element['#message_list'] = str_replace($placeholder, static::$messages, $element['#message_list']);
+    $element['#markup'] = str_replace($placeholder, $markup, $element['#markup']);
+    $element = Renderer::mergeBubbleableMetadata($element, $messages);
 
     return $element;
   }
diff --git a/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php b/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
index 6783632..7dfc02f 100644
--- a/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
@@ -72,35 +72,17 @@ public function defaultConfiguration() {
    * {@inheritdoc}
    */
   public function build() {
-
-    $build['messages'] = array(
-      // @TODO change this to status_messages once the messages are gone from
-      // template_preprocess_page
-      '#theme' => 'status_messages_block',
-      '#pre_render' => array(array($this, 'getMessagesPlaceholder')),
-    );
-    $build['messages']['#status_headings'] = array(
-      'status' => t('Status message'),
-      'error' => t('Error message'),
-      'warning' => t('Warning message'),
-    );
-
-    return $build;
-  }
-
-  /**
-   * Gets messages in the pre-render stage.
-   *
-   * @param $element
-   * @return mixed
-   */
-  public function getMessagesPlaceholder($element) {
     $callback = 'system.messages_post_render_cache:renderMessages';
-    $context = array();
+    $context = [];
     $placeholder = drupal_render_cache_generate_placeholder($callback, $context);
-    $element['#post_render_cache'] = array($callback => array($context));
-    $element['#message_list'] = $placeholder;
-    return $element;
+    return [
+      '#post_render_cache' => array(
+        $callback => array(
+          $context,
+        ),
+      ),
+      '#markup' => $placeholder,
+    ];
   }
 
   /**
diff --git a/core/modules/system/system.services.yml b/core/modules/system/system.services.yml
index 84fb2cb..fd29409 100644
--- a/core/modules/system/system.services.yml
+++ b/core/modules/system/system.services.yml
@@ -44,6 +44,7 @@ services:
       - { name: event_subscriber }
   system.messages_post_render_cache:
     class: Drupal\system\MessagesPostRenderCache
+    arguments: ['@renderer']
   system.theme_settings_cache_tag:
     class: Drupal\system\EventSubscriber\ThemeSettingsCacheTag
     arguments: ['@theme_handler', '@cache_tags.invalidator']