anchor.diff:    }
   
     User _currentUser;
  +
  +  /// Currently signed-in user.
     User get currentUser {
       if (jsObject.currentUser != null) {
         if (_currentUser != null) {
  
positive.code: /// See: <https://firebase.google.com/docs/reference/js/firebase.auth.Auth>.
  class Auth extends JsObjectWrapper<AuthJsImpl> {
    App _app;
    App get app {
      if (_app != null) {
        _app.jsObject = jsObject.app;
  
negative.code:       handleThenableWithMapper(jsObject.linkWithPopup(provider),
            (u) => new UserCredential.fromJsObject(u));
  
    /// Links the authenticated [provider] to the user account using
    /// a full-page redirect flow.
    Future linkWithRedirect(AuthProvider provider) =>
        handleThenable(jsObject.linkWithRedirect(provider));
  
    /// Re-authenticates a user using a fresh [credential]. Should be used
    /// before operations such as [updatePassword()] that require tokens
    /// from recent sign-in attempts.
    Future reauthenticate(AuthCredential credential) =>
        handleThenable(jsObject.reauthenticate(credential));
  
    /// If signed in, it refreshes the current user.
    Future reload() => handleThenable(jsObject.reload());
  
    /// Sends an e-mail verification to a user.
    Future sendEmailVerification() =>
        handleThenable(jsObject.sendEmailVerification());
  
    /// Unlinks a provider with [providerId] from a user account.
    Future<User> unlink(String providerId) => handleThenableWithMapper(
        jsObject.unlink(providerId),
        (firebase_interop.UserJsImpl u) => new User.fromJsObject(u));
  
    /// Updates the user's e-mail address to [newEmail].
    Future updateEmail(String newEmail) =>
        handleThenable(jsObject.updateEmail(newEmail));
  
    /// Updates the user's password to [newPassword].
    /// Requires the user to have recently signed in. If not, ask the user
    /// to authenticate again and then use [reauthenticate()].
    Future updatePassword(String newPassword) =>
        handleThenable(jsObject.updatePassword(newPassword));
  
    /// Updates a user's [profile] data.
    /// UserProfile has a displayName and photoURL.
    ///
    ///     UserProfile profile = new UserProfile(displayName: "Smart user");
    ///     await user.updateProfile(profile);
    Future updateProfile(firebase_interop.UserProfile profile) =>
        handleThenable(jsObject.updateProfile(profile));
  }
  