OO for the sake of OO? No, thanks!

There is no point in turning this into an object! Look again at the resulting API ... it's awkward. It might make sense to implement class Google::Charts that can load the data in several formats (encoded and not encoded or whatever), do something sensible with them, allow you to look at the details and then export the data in some formats ... one of them being this encoded string, but a class that has exactly one method and nothing you could really call internal state is bad design.

Keep it procedural and export the function on request!