Revert "Remove Expect from core library."

tests/standalone/io/test_runner_exit_code_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";
 
 void runTests(String executable, String script, Iterator iterator) {
   if (iterator.moveNext()) {
     var progressIndicator = iterator.current;
     Process.run(executable, [script, progressIndicator]).then((result) {
       Expect.equals(1, result.exitCode);
       if (progressIndicator == 'buildbot') {
         Expect.isTrue(result.stdout.contains("@@@STEP_FAILURE@@@"));
       }
       runTests(executable, script, iterator);
     });
   }
 }
 
 main() {
   var scriptPath = new Path(new Options().script);
   var scriptDirPath = scriptPath.directoryPath;
   var exitCodeScriptPath =
     scriptDirPath.append('test_runner_exit_code_script.dart');
   var script = exitCodeScriptPath.toNativePath();
   var executable = new Options().executable;
   var progressTypes = ['compact', 'color', 'line', 'verbose',
                        'status', 'buildbot'];
   var iterator = progressTypes.iterator;
   runTests(executable, script, iterator);
 }