wp-admin/includes/class-wp-upgrader.php:162Initializes the upgrader.
public function init() { $this->skin->set_upgrader( $this ); $this->generic_strings(); if ( ! wp_installing() ) { $this->schedule_temp_backup_cleanup(); } }Introduced in 2.8.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-wp-upgrader.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.