Revert "Remove Expect from core library."

tests/compiler/dart2js/type_inference_test.dart

 // Copyright (c) 2011, 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 'compiler_helper.dart';
 
 const String TEST_ONE = r"""
 sum(a, b) {
   var c = 0;
   for (var d = a; d < b; d += 1) c = c + d;
   return c;
 }
 """;
 
@@ skipping 91 matching lines @@
   Expect.isTrue(regexp.hasMatch(generated));
   Expect.isTrue(!generated.contains('index'));
   Expect.isTrue(!generated.contains('indexSet'));
 
   generated = compile(TEST_SIX, entry: 'foo');
   regexp = new RegExp('a.constructor !== Array');
   Expect.isTrue(regexp.hasMatch(generated));
   Expect.isTrue(!generated.contains('index'));
   Expect.isTrue(!generated.contains('indexSet'));
 }