Revert "Remove Expect from core library."

tests/standalone/io/process_check_arguments_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 "process_test_util.dart";
 
 test(args) {
   var future = Process.start(new Options().executable, args);
   future.then((process) {
     process.exitCode.then((exitCode) {
       Expect.equals(0, exitCode);
     });
     // Drain stdout and stderr.
@@ skipping 14 matching lines @@
   test([scriptFile.path, '3', '0', 'a b']);
   test([scriptFile.path, '3', '0', 'a\tb']);
   test([scriptFile.path, '3', '1', 'a\tb"']);
   test([scriptFile.path, '3', '1', 'a"\tb']);
   test([scriptFile.path, '3', '1', 'a"\t\\\\"b"']);
   test([scriptFile.path, '4', '0', 'a\tb', 'a']);
   test([scriptFile.path, '4', '0', 'a\tb', 'a\t\t\t\tb']);
   test([scriptFile.path, '4', '0', 'a\tb', 'a    b']);
 }