Files: wp-admin/includes/class-plugin-upgrader.php

Turns off maintenance mode after upgrading an active plugin.

Turns on maintenance mode before attempting to background update an active plugin.

Deactivates a plugin before it is upgraded.

Retrieve the path to the file that contains the plugin info.

Check a source package to be sure it contains a plugin.

Bulk upgrade several plugins at once.

Upgrade a plugin.

Install a plugin package.

Initialize the installation strings.

Initialize the upgrade strings.