Revert "Remove Expect from core library."

tests/language/const_list_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";
-
 class ConstListTest {
 
   static testMain() {
     List fixedList = new List(4);
     List fixedList2 = new List(4);
     List growableList = new List();
     List growableList2 = new List();
     for (int i = 0; i < 4; i++) {
       fixedList[i] = i;
       fixedList2[i] = i;
@@ skipping 16 matching lines @@
     Expect.equals(false, a == b);
     a = const [1, 2, 3.1];
     b = const [1, 2, 3.1];
     Expect.equals(true, a == b);
   }
 }
 
 main() {
   ConstListTest.testMain();
 }