pkg/http: updated unittest dependency, removed unused imports

pkg/http/test/html/streamed_request_test.dart

 // Copyright (c) 2014, 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 http.test.html.streamed_request_test;
 
-import 'dart:convert';
-
 import 'package:http/http.dart' as http;
 import 'package:http/browser_client.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 void main() {
   group('contentLength', () {
     test("works when it's set", () {
       var request = new http.StreamedRequest('POST', echoUrl);
@@ skipping 11 matching lines @@
       var request = new http.StreamedRequest('POST', echoUrl);
       request.sink.add([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
       request.sink.close();
 
       return new BrowserClient().send(request).then((response) {
         expect(response.stream.toBytes(),
             completion(equals([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])));
       });
     });
   });
-}
+}