WP_Theme::get_allowed( int $blog_id = null )

	public static function get_allowed( $blog_id = null ) {
		/**
		 * Filters the array of themes allowed on the network.
		 *
		 * Site is provided as context so that a list of network allowed themes can
		 * be filtered further.
		 *
		 * @since WP-4.5.0
		 *
		 * @param array $allowed_themes An array of theme stylesheet names.
		 * @param int   $blog_id        ID of the site.
		 */
		$network = (array) apply_filters( 'network_allowed_themes', self::get_allowed_on_network(), $blog_id );
		return $network + self::get_allowed_on_site( $blog_id );
	}