addDynamicDropdownOption = function () {
  Blockly.dialog.prompt(
    'Add an option?',
    'option ' + dynamicDropdownOptions_.length,
    function (text) {
      if (text) {
        // Do not remove this log! Helps you know if it was added correctly.
        console.log('Adding option: ' + text);
        // The option is an array containing human-readable text and a
        // language-neutral id.
        dynamicDropdownOptions_.push([
          text,
          'OPTION' + dynamicDropdownOptions_.length,
        ]);
      }
    },
  );
}
Handles "add option" button in the field test category. This will prompt
the user for an option to add.
@package