In the code:
var fromAddress = {
enabled: true,
street: '',
city: '',
state: '',
zip: '',
country: '',
full: ''
};
i can see that you have enabled driving directions, but you have not provided a starting address.
if you want to allow the site visitor to enter an address, you will need to create a form on the page, and bind the address elements to the form.
see the "Displaying Driving Directions" and "Displaying Form Elements" tutorials in the Solution recipes section of the pro maps support page:
pro-maps-for-google/