Source

File: wp-includes/customize/class-wp-customize-selective-refresh.php

public function __construct( WP_Customize_Manager $manager ) {
		$this->manager = $manager;
		require_once ABSPATH . WPINC . '/customize/class-wp-customize-partial.php';

		add_action( 'customize_preview_init', array( $this, 'init_preview' ) );
	}