onUpgrade = function(rawDb) {
    return new Promise(function(resolve, reject) {
      try {
        assertMethods(rawDb, [
          'getRawDBInstance', 'getRawTransaction', 'dropTable',
          'addTableColumn', 'dropTableColumn', 'renameTableColumn',
          'createRow', 'getVersion', 'dump'
        ], 'raw.BackStore');
      } catch (e) {
        reject(e);
      }
      resolve();
    });
  }
Tests lf.raw.BackStore API.
@return {!IThenable}