function createSettings(rules) {
  var settings = new pluginSettings.Settings('myplugin');
  if (rules) {
    for (var pattern in rules) {
      settings.set(pattern, rules[pattern], function() {});
    }
  }
  return settings;
}
Creates a new Settings object with a set of rules for a dummy plugin.
Because we provide stub implementations for the Chrome contentSettings
extension API, we know that the methods will execute immediately instead of
asynchronously.
@param {!Object} rules A map from content settings pattern to setting.
@return {!pluginSettings.Settings} A newly created Settings object with the
    passed in set of rules.