getKeysDescription_(keys) {
    return goog.array.flatten(goog.array.map(keys, function(key) {
      var type =
          (key.key.secret ? chrome.i18n.getMessage('secretKeyDescription') :
                            chrome.i18n.getMessage('publicKeyDescription'));
      return [{
        type: type,
        algorithm: key.key.algorithm,
        fingerprint: key.key.fingerprintHex
      }];
    }));
  }
Returns a human readable representation of the given collection of PGP
keys.
@param {Array} keys Raw collection of PGP keys.
@return {!Array} A collection of PGP key metadata.
@private