Undefined class 'AuthResult' in Flutter

Starting from Version firebase_auth 0.18.0:

FirebaseUser has been changed to User

AuthResult has been changed to UserCredential

GoogleAuthProvider.getCredential() has been changed to GoogleAuthProvider.credential()

onAuthStateChanged which notifies about changes to the user's sign-in state was replaced with authStateChanges()

currentUser() which is a method to retrieve the currently logged in user, was replaced with the property currentUser and it no longer returns a Future<FirebaseUser>

They renamed the class AuthResult to UserCredential

The problem was firebase_auth version that I added to pubspec.yaml.

Previous version I have been using: firebase_auth: ^0.11.1+8

Now: firebase_auth: ^0.15.2

This change on versions has fixed the problem.