grpc-web request from linux client

Hi,
I would like to be able to make grpc-web requests from linux client. This requires xhr from linux. But grpc-web dependencies only exist in web. (grpc or grpcweb channel, for instance)

To circumvent this behavior, I tried to use universa_-html, a package that provides xhr on non-web platforms, but got some errors that might need further debugging/development. A fork exists with such modifications.

I think it might be useful to have this feature, in order to make testing grpc-web clients easier.

Start by reviewing the issue's Linux-client requirement, the grpc or grpcweb channel dependencies, and the referenced universa_-html fork. Determine which platform constraints and errors must be addressed; done means grpc-web requests work from a Linux Dart client and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.