setUser(props) {
    if (props) {
      // User is logged in.
      for (var key in FakeAuthClient.UserProperty) {
        var prop = FakeAuthClient.UserProperty[key];
        this.user_[prop] = props[prop];
      }
      this['currentUser'] = this.user_;
    } else {
      // User is logged out.
      this['currentUser'] = null;
    }
  }
Updates the user with selected properties.
@param {!Object} props The updated user properties, if null, user is
    nullified.