function progressed(update) {
		return new Promise(function (type, args, _, notify) {
			var onProgress = args[2];
			try {
				notify(typeof onProgress === 'function' ? onProgress(update) : update);
			} catch(e) {
				notify(e);
			}
		});
	}
Create a progress promise with the supplied update.
@private
@param {*} update
@return {Promise} progress promise