Revert "Remove Expect from core library."

tests/compiler/dart2js/boolified_operator_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.
 
 library boolified_operator_test;
-import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 
 const String TEST_EQUAL = r"""
 foo(param0, param1) {
   if (param0 == param1) return 0;
   return 1;
 }
 """;
 
 const String TEST_EQUAL_NULL = r"""
@@ skipping 50 matching lines @@
   Expect.isTrue(generated.contains('leB'));
   
   generated = compile(TEST_GREATER, entry: 'foo');
   Expect.isFalse(generated.contains('=== true'));
   Expect.isTrue(generated.contains('gtB'));
   
   generated = compile(TEST_GREATER_EQUAL, entry: 'foo');
   Expect.isFalse(generated.contains('=== true'));
   Expect.isTrue(generated.contains('geB'));
 }