Revert "Remove Expect from core library."

tests/language/list_literal2_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.
 // Test program for array literals.
 
-import "package:expect/expect.dart";
-
 class ArrayLiteral2Test {
   static const int LAUREL = 1965;
   static const int HARDY = 1957;
 
   static const LUCKY_DOG = const <int>[ 1919, 1921 ];
   static const MUSIC_BOX = const [ LAUREL, HARDY ];
 
   static testMain() {
     Expect.equals(2, LUCKY_DOG.length);
     Expect.equals(2, MUSIC_BOX.length);
 
     Expect.equals(1919, LUCKY_DOG[0]);
     Expect.equals(1921, LUCKY_DOG[1]);
 
     Expect.equals(LAUREL, MUSIC_BOX[0]);
     Expect.equals(HARDY, MUSIC_BOX[1]);
   }
 }
 
 main() {
   ArrayLiteral2Test.testMain();
 }