isEmailSignUpDisabled() {
    // This is only applicable to email.
    const emailSignInOption = this.getSignInOptionsForProvider_(
        firebase.auth.EmailAuthProvider.PROVIDER_ID);
    return !!(emailSignInOption &&
              emailSignInOption['disableSignUp'] &&
              emailSignInOption['disableSignUp']['status']);
  }
@return {boolean} Whether the user is disabled to sign up with email.