anchor.diff:  /// See: <https://firebase.google.com/docs/reference/js/firebase.auth.Auth>.
   class Auth extends JsObjectWrapper<AuthJsImpl> {
     App _app;
  +
  +  /// App for this instance of auth service.
     App get app {
       if (_app != null) {
         _app.jsObject = jsObject.app;
  
positive.code:       handleThenableWithMapper(jsObject.linkWithPopup(provider),
            (u) => new UserCredential.fromJsObject(u));
  
    Future linkWithRedirect(AuthProvider provider) =>
        handleThenable(jsObject.linkWithRedirect(provider));
  
    Future reauthenticate(AuthCredential credential) =>
        handleThenable(jsObject.reauthenticate(credential));
  
    Future reload() => handleThenable(jsObject.reload());
  
    Future sendEmailVerification() =>
        handleThenable(jsObject.sendEmailVerification());
  
    Future<User> unlink(String providerId) => handleThenableWithMapper(
        jsObject.unlink(providerId),
        (firebase_interop.UserJsImpl u) => new User.fromJsObject(u));
  
    Future updateEmail(String newEmail) =>
        handleThenable(jsObject.updateEmail(newEmail));
  
    Future updatePassword(String newPassword) =>
        handleThenable(jsObject.updatePassword(newPassword));
  
    Future updateProfile(firebase_interop.UserProfile profile) =>
        handleThenable(jsObject.updateProfile(profile));
  }
  
negative.code:   }
  
    User _currentUser;
  
    /// Currently signed-in user.
    User get currentUser {
      if (jsObject.currentUser != null) {
        if (_currentUser != null) {
  