function getTopics() {
  var topics = JSON.parse(window.localStorage.getItem('topics'));
  var keywords = JSON.parse(window.localStorage.getItem('keywords'));
  var element = $('topics');

  // Sets all topics as default list if no list is found from local storage.
  if (!topics && !keywords) {
    topics = [' ','n','w','b','t','e','s','m','po'];
  }

  if (topics) {
    for (var i = 0; i < (topics.length); i++) {
      var val = (topics[i] == ' ') ? '1' : topics[i];
      element.options[element.options.length] = new Option(
          chrome.i18n.getMessage(val), topics[i]);
    }
  }

  // Shows custom topics in list(if any).
  if (keywords) {
    for (i = 0; i < (keywords.length); i++) {
      element.options[element.options.length] = new Option(keywords[i],
          keywords[i]);
    }
  }

  $('option_link').innerText = chrome.i18n.getMessage('options');

  var topicVal = window.localStorage.getItem('lastTopic');
  if (topicVal) {
    $('topics').value = topicVal;
  }
}
Shows topic list retrieved from local storage(if any),else shows
default topics list.