code: function() {
        var auth = this._auth;
  
        return this._q(function(resolve) {
          var off;
          function callback() {
            // Turn off this onAuthStateChanged() callback since we just needed to get the authentication data once.
            off();
            resolve();
          }
          off = auth.onAuthStateChanged(callback);
        });
      }
docs: Helper that returns a promise which resolves when the initial auth state has been
  fetched from the Firebase server. This never rejects and resolves to undefined.
  
  @return {Promise<Object>} A promise fulfilled when the server returns initial auth state.