Feature request: Add factory constructor to HttpHeaders interface

[cah4a]

I'm working on a server mocking library. Something like nock for Javascript, but for Dart/Flutter.

I have an issue with constructing HttpHeaders because package dart:http doesn't provide any constructor for it.

Thus, I have to either implement all the functionality by myself, either use a weird workaround:

Future<HttpHeaders> createHeaders() async {
    final request = await originalHttpClient.head("localhost", 0, "");
    return request.headers;
}

Both solutions are not so good and have disadvantages.