function insertSampleData() {
  var generateRowsForTable = function(table) {
    var sampleDataCount = 3;
    var rows = new Array(sampleDataCount);
    for (var i = 0; i < sampleDataCount; i++) {
      rows[i] = table.createRow({
        'id': i,
        'name': 'dummyName' + i.toString()
      });
    }
    return rows;
  };

  tableARows = generateRowsForTable(ta);
  tableBRows = generateRowsForTable(tb);

  var tx = env.db.createTransaction();
  return tx.exec([
    env.db.insert().into(ta).values(tableARows),
    env.db.insert().into(tb).values(tableBRows)
  ]);
}
Inserts 3 sample rows to the database, for each table.
@return {!IThenable}