storefront/inc/customizer/class-storefront-customizer-control-arbitrary.php

<?php
/**
 * Class to create a custom arbitrary html control for dividers etc
 */
class Arbitrary_Storefront_Control extends WP_Customize_Control {
	public $settings 	= 'blogname';
	public $description = '';

	public function render_content() {
		switch ( $this->type ) {
			default:
			case 'text' :
				echo '<p class="description">' . wp_kses_post( $this->description ) . '</p>';
			break;

			case 'heading':
				echo '<span class="customize-control-title">' . esc_html( $this->label ) . '</span>';
			break;

			case 'divider' :
				echo '<hr style="margin: 1em 0;" />';
			break;
		}
	}
}