wp-admin/includes/class-wp-upgrader.php:143Construct the upgrader with a skin.
$skinWP_Upgrader_Skinoptionalnull public function __construct( $skin = null ) { if ( null === $skin ) { $this->skin = new WP_Upgrader_Skin(); } else { $this->skin = $skin; } }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.