Add 'Server' and 'User-Agent' default header fields.

pkg/http/test/client_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library client_test;
 
 import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:http/src/utils.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 void main() {
   tearDown(stopServer);
 
   test('#send a StreamedRequest', () {
     expect(startServer().then((_) {
       var client = new http.Client();
       var request = new http.StreamedRequest("POST", serverUrl);
       request.headers[HttpHeaders.CONTENT_TYPE] =
         'application/json; charset=utf-8';
+      request.headers[HttpHeaders.USER_AGENT] = 'Dart';
 
       expect(client.send(request).then((response) {
         expect(response.request, equals(request));
         expect(response.statusCode, equals(200));
         expect(response.headers['single'], equals('value'));
         // dart:io internally normalizes outgoing headers so that they never
         // have multiple headers with the same name, so there's no way to test
         // whether we handle that case correctly.
 
         return response.stream.bytesToString();
       }).whenComplete(client.close), completion(parse(equals({
         'method': 'POST',
         'path': '/',
         'headers': {
           'content-type': ['application/json; charset=utf-8'],
           'accept-encoding': ['gzip'],
+          'user-agent': ['Dart'],
           'transfer-encoding': ['chunked']
         },
         'body': '{"hello": "world"}'
       }))));
 
       request.sink.add('{"hello": "world"}'.codeUnits);
       request.sink.close();
     }), completes);
   });
 
   test('#send with an invalid URL', () {
     expect(startServer().then((_) {
       var client = new http.Client();
       var url = Uri.parse('http://http.invalid');
       var request = new http.StreamedRequest("POST", url);
       request.headers[HttpHeaders.CONTENT_TYPE] =
           'application/json; charset=utf-8';
 
       expect(client.send(request), throwsSocketIOException);
 
       request.sink.add('{"hello": "world"}'.codeUnits);
       request.sink.close();
     }), completes);
   });
 }