Remove Expect from core library.

tests/corelib/iterable_to_list_test.dart

 // Copyright (c) 2012, 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";
+
 main() {
   List<int> list1 = <int>[1, 2, 3];
   List<int> list2 = const <int>[4, 5];
   List<String> list3 = <String>[];
   Set<int> set1 = new Set<int>();
   set1..add(11)
       ..add(12)
       ..add(13);
   Set<String> set2 = new Set<String>();
   set2..add("foo")
@@ skipping 33 matching lines @@
   Expect.isTrue(listCopy.contains("bar"));
   Expect.isTrue(listCopy.contains("toto"));
   Expect.isTrue(listCopy is List<String>);
   Expect.isFalse(listCopy is List<int>);
 
   listCopy = set3.toList();
   Expect.isTrue(listCopy.isEmpty);
   Expect.isTrue(listCopy is List<int>);
   Expect.isTrue(listCopy is List<String>);
 }