Issue #3493911: Add a CachedPlaceholderStrategy and use a placeholder to...

Issue #3493911: Add a CachedPlaceholderStrategy and use a placeholder to render the navigation toolbar

Closes #3504902

core/lib/Drupal/Core/Cache/ApcuBackend.php

@@ -98,6 +98,18 @@ public function getMultiple(&$cids, $allow_invalid = FALSE) {
     $result = apcu_fetch(array_keys($map));
     $cache = [];
     if ($result) {
+      // Before checking the validity of each item individually, register the
+      // cache tags for all returned cache items for preloading, this allows the
+      // cache tag service to optimize cache tag lookups.
+      if ($this->checksumProvider instanceof CacheTagsChecksumPreloadInterface) {
+        $tags_for_preload = [];
+        foreach ($result as $item) {
+          if ($item->tags) {
+            $tags_for_preload[] = explode(' ', $item->tags);
+          }
+        }
+        $this->checksumProvider->registerCacheTagsForPreload(array_merge(...$tags_for_preload));
+      }
       foreach ($result as $key => $item) {
         $item = $this->prepareItem($item, $allow_invalid);
         if ($item) {