Check if the page has a gravity form

has-gform.php

<?php
/**
 * Check if the page has a gravity form.
 *
 * @since 1.0.0
 *
 * @param int $id Post or page id, default to false.
 *
 * @return boolean
 */
if( !function_exists( 'has_gform' ) ) {
	function has_gform( $id = false ) {
		if( !$id ) global $post;
		else $post = get_post( $id );
		return isset( $post->post_content ) ? ( strpos( $post->post_content,'[gravityform' ) !== false ) : false;
	}
}