Revert "Remove Expect from core library."

tests/language/list_literal3_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.
 // Check that arrays from const array literals are immutable.
 
-import "package:expect/expect.dart";
-
 class ListLiteral3Test {
 
   static const List<String> canonicalJoke = const ["knock", "knock"];
 
   static testMain() {
 
     List<String> joke = const ["knock", "knock"];
     // Elements of canonical lists are canonicalized.
     Expect.identical(joke, canonicalJoke);
     Expect.identical(joke[0], joke[1]);
@@ skipping 22 matching lines @@
     Expect.identical(b[0], b[1]);
     Expect.equals(true, b[0][0] == 1.0);
     Expect.identical(b[0][0], b[1][0]);
     Expect.throws(() { b[0][0] = 42.0; }, (e) => e is UnsupportedError);
   }
 }
 
 main() {
   ListLiteral3Test.testMain();
 }