search(code) {
    // Get all keys and prefixes.
    var keyAndPrefixes = this.trie_.getKeyAndPrefixes(code);
    // Get matching key and prefixes.
    for (var key in keyAndPrefixes) {
      if (keyAndPrefixes.hasOwnProperty(key)) {
        // Pick first one. There should always be one as country codes can't be
        // prefixes of each other.
        return keyAndPrefixes[key];
      }
    }
    return [];
  }
Looks up the country that matches the code's prefix.
@param {string} code The string that could contain a country code prefix.
@return {!Array<!firebaseui.auth.data.country.Country>} The country objects
    that match the prefix of the code provided, empty array if not found.