Add request body to http request function in http library

[DartBot]

<img src="https://avatars.githubusercontent.com/u/1688987?v=3" align="left" width="96" height="96"hspace="10"> Issue by luisvt
Originally opened as dart-lang/sdk#20839

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Add the ability to send http request body to delete function on http library (https://pub.dartlang.org/packages/http).

I was trying to use next code:

      delete('http://127.0.0.1:4040/persons', body: '[1,2]').then((Response response) {
        //... other code ...
      });

I realize that it wasn't possible to do it since the function doesn't support a request body. So instead, I should use next code:

      new Client().send(new Request('DELETE', new Uri.http('127.0.0.1:4040', '/persons'))..body = '[1,2]').then((response) {
        //... other code ...
      });

Although is not a big problem on doing in the second way all the time, it would be great to be able on doing in the first way.

I know that you should modify lines 107 and 108 on file http from this:

  Future<Uint8List> delete(url, {Map<String, String> headers}) =>
    _withClient((client) => client.delete(url, headers: headers));

to this:

  Future<Uint8List> delete(url, {Map<String, String> headers, body}) =>
    _withClient((client) => client.delete(url, headers: headers, body));

also line 96 on client.dart from this:

  Future<Response> delete(url, {Map<String, String> headers});

to this:
  Future<Response> delete(url, {Map<String, String> headers, body});

and also lines 85 and 86 in base_client.dart from this:

  Future<Response> delete(url, {Map<String, String> headers}) =>
    _sendUnstreamed("DELETE", url, headers);

to this:

  Future<Response> delete(url, {Map<String, String> headers, body}) =>
    _sendUnstreamed("DELETE", url, headers, body);

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Removed Type-Defect label.
Added Type-Enhancement, Area-Pkg, Pkg-Http, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

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It's very rare to want to send a DELETE request with a body, and the semantics aren't very clear. The top-level methods are intended to be used for common use-cases, but there's nothing wrong with constructing an explicit Request if you're doing something out of the ordinary.

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Added NotPlanned label.