Revert "Remove Expect from core library."

tests/standalone/io/process_environment_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.
 
-import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 import "process_test_util.dart";
 
 runEnvironmentProcess(Map environment, name, callback) {
   var dartExecutable = new Options().executable;
   var options = new ProcessOptions();
   options.environment = environment;
   var printEnv = 'tests/standalone/io/print_env.dart';
   if (!new File(printEnv).existsSync()) {
@@ skipping 29 matching lines @@
     });
     // Only check one value to not spin up too many processes testing the
     // same things.
     break;
   }
 }
 
 main() {
   testEnvironment();
 }