compiler/natives/src/net/http: Close request body in XHRTransport.

The http.RoundTripper interface (https://godoc.org/net/http#RoundTripper) says:

	// RoundTrip should not modify the request, except for
	// consuming and closing the Request's Body.
	//
	// RoundTrip must always close the body, including on errors,
	// but depending on the implementation may do so in a separate
	// goroutine even after RoundTrip returns.

Close request body in XHRTransport.RoundTrip to satisfy the interface contract.

Author: dmitshur

compiler/natives/src/net/http/http.go

@@ -79,8 +79,10 @@ func (t *XHRTransport) RoundTrip(req *Request) (*Response, error) {
 		var err error
 		body, err = ioutil.ReadAll(req.Body)
 		if err != nil {
+			req.Body.Close() // RoundTrip must always close the body, including on errors.
 			return nil, err
 		}
+		req.Body.Close()
 	}
 	xhr.Call("send", body)