Custom_Image_Header::customize_set_last_used( WP_Customize_Manager $wp_customize )

	public function customize_set_last_used( $wp_customize ) {

		$header_image_data_setting = $wp_customize->get_setting( 'header_image_data' );
		if ( ! $header_image_data_setting ) {
			return;
		}
		$data = $header_image_data_setting->post_value();

		if ( ! isset( $data['attachment_id'] ) ) {
			return;
		}

		$attachment_id = $data['attachment_id'];
		$key = '_wp_attachment_custom_header_last_used_' . get_stylesheet();
		update_post_meta( $attachment_id, $key, time() );
	}