Right now the Google Sign In plugin isn't adequately integration tested.

The iOS version of the example requires following the signup steps in the README or it won't work. Because we don't necessarily want everyone sharing the same GoogleService-Info.plist, we might want to write the file using Cirrus encypted data. Perhaps there's another solution that can run on non-Cirrus infrastructure.

We'll also need the EarlGrey bindings for Flutter.