Revert "Remove Expect from core library."

tests/corelib/collection_from_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.
 
 library collection.from.test;
-import "package:expect/expect.dart";
 import 'dart:collection' show Queue;
 
 class CollectionFromTest {
   static testMain() {
     var set = new Set<int>();
     set.add(1);
     set.add(2);
     set.add(4);
     check(set, new List<int>.from(set));
     check(set, new List.from(set));
@@ skipping 14 matching lines @@
     initial.forEach((e) { initialSum += e; });
     other.forEach((e) { otherSum += e; });
     Expect.equals(4 + 2 + 1, otherSum);
     Expect.equals(otherSum, initialSum);
   }
 }
 
 main() {
   CollectionFromTest.testMain();
 }