The goal for this test should be to serve as an example of connecting to a service in //ios/chrome (as well as a guard against regressions, of course).

The test can be of connecting to the Identity Service: It can connect to Identity Manager after having populated PO2TS/SigninManager with expected information and check that the expected information is there.

Note that we'll have to host the Identity Service in //ios/chrome to enable this. It's not clear offhand whether we should do that hosting in production code or just set it up in the test for now.