Use shelf in pub's barback and admin servers.

sdk/lib/_internal/pub/test/oauth2/utils.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 oauth2.utils;
 
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:shelf/shelf.dart' as shelf;
 
-import '../../lib/src/io.dart';
 import '../../lib/src/utils.dart';
 
 void authorizePub(ScheduledProcess pub, ScheduledServer server,
     [String accessToken="access token"]) {
   pub.stdout.expect('Pub needs your authorization to upload packages on your '
       'behalf.');
 
   schedule(() {
     return pub.stdout.next().then((line) {
       var match = new RegExp(r'[?&]redirect_uri=([0-9a-zA-Z.%+-]+)[$&]')
@@ skipping 19 matching lines @@
       expect(body, matches(new RegExp(r'(^|&)code=access\+code(&|$)')));
 
       return new shelf.Response.ok(JSON.encode({
         "access_token": accessToken,
         "token_type": "bearer"
       }), headers: {'content-type': 'application/json'});
     });
   });
 }