code: function addSetValues(args) {
    for (var key in args.from) {
      if (args.from[key]) {
        args.to[key] = true;
      }
    }
  }
docs: Makes 'to' the set union of 'from' and 'to'.
  @param {!{from: !Object.<string, boolean>, to: !Object.<string, boolean>}}
  args