Revert "Remove Expect from core library."

tests/standalone/io/directory_error_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.
 //
 // Dart test program for testing error handling in directory I/O.
 
-import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 Directory tempDir() {
   return new Directory('').createTempSync();
 }
 
 
 bool checkCreateInNonExistentFileException(e) {
@@ skipping 201 matching lines @@
 main() {
   runTest(testCreateInNonExistent);
   runTest(testCreateTempInNonExistent);
   runTest(testDeleteNonExistent);
   runTest(testDeleteRecursivelyNonExistent);
   runTest(testListNonExistent);
   runTest(testRenameNonExistent);
   runTest(testRenameFileAsDirectory);
   runTest(testRenameOverwriteFile);
 }