- This class is a subclass of OAuth2TokenService.
- It is ChromeOS-specific and satisfies requests for access tokens by getting them off the device in some fashion.
- If it's *not* going to be in the Identity Service, we'll need to figure out how to decouple it from OAuth2TokenService, since OAuth2TokenService *will* become part of the internal implementation of the Identity Service in the long term.
- Not clear how to handle this offhand.