Revert "Remove Expect from core library."

tests/compiler/dart2js/builtin_interceptor_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"""
 foo(String a) {
   // Make sure the string class is registered.
   var c = 'foo';
   // index into the parameter and move into a loop to make sure we'll get a
   // type guard.
   for (int i = 0; i < 1; i++) {
     print(a[0] + c);
@@ skipping 26 matching lines @@
 
   generated = compile(TEST_TWO, entry: 'foo');
   Expect.isTrue(generated.contains("return 3;"));
 
   generated = compile(TEST_THREE, entry: 'foo');
   Expect.isTrue(generated.contains("return 3;"));
 
   generated = compile(TEST_FOUR, entry: 'foo');
   Expect.isTrue(generated.contains("push(2);"));
 }