Source

File: wp-includes/class-wp-customize-control.php

/**
 * WP_Customize_Theme_Control class.
 */
require_once ABSPATH . WPINC . '/customize/class-wp-customize-theme-control.php';

/**
 * WP_Widget_Area_Customize_Control class.
 */
require_once ABSPATH . WPINC . '/customize/class-wp-widget-area-customize-control.php';

/**
 * WP_Widget_Form_Customize_Control class.
 */
require_once ABSPATH . WPINC . '/customize/class-wp-widget-form-customize-control.php';