Reapply "Add a sleep function to dart:io"

utils/tests/pub/test_pub.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.
 
 /// Test infrastructure for testing pub. Unlike typical unit tests, most pub
 /// tests are integration tests that stage some stuff on the file system, run
 /// pub, and then validate the results. This library provides an API to build
 /// tests like that.
 library test_pub;
 
 import 'dart:async';
 import 'dart:collection' show Queue;
-import 'dart:io';
+import 'dart:io' hide sleep;
 import 'dart:json' as json;
 import 'dart:math';
 import 'dart:uri';
 import 'dart:utf';
 
 import 'package:http/testing.dart';
 import 'package:oauth2/oauth2.dart' as oauth2;
 import 'package:pathos/path.dart' as path;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_server.dart';
@@ skipping 581 matching lines @@
   bool matches(item, MatchState matchState) {
     if (item is! Pair) return false;
     return _firstMatcher.matches(item.first, matchState) &&
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }