Convert pkg/http to use "package:" imports.

pkg/http/test/http_test.dart

 // Copyright (c) 2012, 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;
 
 import 'dart:io';
 
-import '../../unittest/lib/unittest.dart';
-import '../lib/http.dart' as http;
+import 'package:unittest/unittest.dart';
+import 'package:http/http.dart' as http;
 import 'utils.dart';
 
 main() {
   group('http.', () {
     setUp(startServer);
     tearDown(stopServer);
 
     test('head', () {
       expect(http.head(serverUrl).transform((response) {
         expect(response.statusCode, equals(200));
@@ skipping 161 matching lines @@
           'x-other-header': ['Other Value']
         },
       }))));
     });
 
     test('readBytes throws an error for a 4** status code', () {
       expect(http.readBytes(serverUrl.resolve('/error')), throwsHttpException);
     });
   });
 }