function insertData(filename, tableSchema) {
  return getSampleData(filename).then(
      function(data) {
        var rows = data.map(function(obj) {
          return tableSchema.createRow(obj);
        });
        return db.insert().into(tableSchema).values(rows);
      });
}
Inserts data in the database.
@param {string} filename The name of the file holding JSON data.
@param {!lf.schema.Table} tableSchema The schema of the table corresponding
    to the data.
@return {!IThenable<!lf.query.Insert>}