Test new scheduled task
Log in as admin.
Go to Site administration > Server > Tasks > Scheduled tasks
Search for chat .
Make sure a new scheduled task for Chat is now available:
Background processing for chat module \mod_chat\task\cron_task
Make sure you are able to edit (Cog icon) and see the logs (That other sheet icon).
Test deprecations
Run:
php admin/tool/task/cli/schedule_task.php --execute="\core\task\legacy_plugin_cron_task"
Make sure you don't get any debugging related to deprecation of chat_cron().