anchor.diff:    }
   
     void _add(String name, Object value) {
  +    var lowerCaseName = name.toLowerCase();
       // TODO(sgjesse): Add immutable state throw HttpException is immutable.
  -    if (name.toLowerCase() == "date") {
  +    if (lowerCaseName == "date") {
         if (value is Date) {
           date = value;
         } else if (value is String) {
  
positive.code:       } else {
          throw new HttpException("Unexpected type for header named $name");
        }
      } else if (name.toLowerCase() == "expires") {
        if (value is Date) {
          expires = value;
        } else if (value is String) {
  
negative.code:       } else {
          throw new HttpException("Unexpected type for header named $name");
        }
      } else if (lowerCaseName == "host") {
        int pos = value.indexOf(":");
        if (pos == -1) {
          _host = value;
  