chrome_pages.cc DCHECKS(SigninManager::IsSigninAllowed()) when showing a browser signin window. SigninManager::IsSigninAllowed() just checks a pref. This method is used in SigninManager itself as well. We'll do this conversion after determining the picture for prefs shared between the Identity Service impl and clients.

chrome_pages.cc also calls SigninManager::IsAuthenticated() to determine whether to show settings or a signin page. This can just be converted to talk to the IdentityManager.

There are also tests that have dependencies that need to be converted.