"History" (last viewed / new markers) functionality has been moved into a separate History module

In Drupal 7, Node module contained built-in API functions for determining the timestamp a registered user has last viewed a particular node. Comment module leveraged the node last viewed data to add "new" markers to new/unread comments.

This functionality has been moved into a separate History module (history.module), so as to decouple it from Node module and potentially make it available for other entity types.

Drupal 7

define('NODE_NEW_LIMIT', REQUEST_TIME - 30 * 24 * 60 * 60);
...
     // Retrieve the timestamp at which the current user last viewed this node.
     if (!$timestamp) {
       $timestamp = node_last_viewed($nid);
     }
...
   // Update the history table, stating that this user viewed this node.
   node_tag_new($node);

Drupal 8

define('HISTORY_READ_LIMIT', REQUEST_TIME - 30 * 24 * 60 * 60);
...
     // Retrieve the timestamp at which the current user last viewed this node.
     if (!$timestamp) {
       $timestamp = history_read($nid);
     }
...
   // Update the history table, stating that this user viewed this node.
   if (module_exists('history')) {
     history_write($node->nid);
   }