ensure_endpoint: function() {
    if (!navigator.push) {
      // Do nothing when push notifications are not supported
      console.log('no support for push notifications');
      return Promise.resolve();
    }

    if (ensure_endpoint_in_progress) {
      return Promise.resolve();
    }
    ensure_endpoint_in_progress = true;

    function ensure_endpoint_done() {
      ensure_endpoint_in_progress = false;
    }

    return asyncStorage.getItem(ENDPOINT_ID_KEY).then(function(endpoint) {
      if (endpoint) {
        return Promise.resolve();
      }

      var defer = Utils.defer();
      var req = navigator.push.register();
      req.onsuccess = function() {
        defer.resolve(req.result);
      };
      req.onerror = function() {
        defer.reject();
      };

      return defer.promise.then(function(endpoint_url) {
        var set_promise = asyncStorage.setItem(ENDPOINT_ID_KEY, endpoint_url);
        return Promise.all([endpoint_url, set_promise]);
      }).then(function(endpoint_url) {
        return SumoDB.register_push_endpoint(endpoint_url);
      }).catch(function() {
        return asyncStorage.removeItem(ENDPOINT_ID_KEY);
      });
    }).then(ensure_endpoint_done, ensure_endpoint_done);
  },