system_update_1057 in core/modules/system/system.install

Add default for watchdog_enabled_severity_levels.

watchdog_severity_enabled in core/includes/bootstrap.inc

Check if logging is enabled for a given severity level.

watchdog_severity_levels in core/includes/common.inc

Returns a list of severity levels, as defined in RFC 3164.

_backdrop_shutdown_function in core/includes/bootstrap.inc

Executes registered shutdown functions.