WP_Customize_Manager::add_customize_screen_to_heartbeat_settings( array $settings )

Source

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

public function add_customize_screen_to_heartbeat_settings( $settings ) {
		global $pagenow;
		if ( 'customize.php' === $pagenow ) {
			$settings['screenId'] = 'customize';
		}
		return $settings;
	}