code: function() {
          return Promise.all([
              this._loadAccountData(),
              this._loadSyncData(),
          ]).then(([accountData, syncData]) => {
              console.log(
                  `LocalIndexedDBStoreBackend: loaded initial data`,
              );
              this._syncAccumulator.accumulate({
                  next_batch: syncData.nextBatch,
                  rooms: syncData.roomsData,
                  groups: syncData.groupsData,
                  account_data: {
                      events: accountData,
                  },
              });
          });
      }
docs: Having connected, load initial data from the database and prepare for use
  @return {Promise} Resolves on success