Let's be clear here: this is an unauthorized use of Google servers.

Unless Google provides an explicit Terms Of Service for this API endpoints allowing its use, you can assume that it exists only to serve Google-owned software (like Chrome).

Just because it exists doesn't mean you can use it.

There's an obvious risk that Google can modify the API and less obvious legal risk of misusing someone else's resources.

Doesn't mean you can't play with it and use it for experiments but you probably shouldn't cross the line of actually using it in any production software.