Revert "Remove Expect from core library."

tests/corelib/iterable_expand_test.dart

Index: tests/corelib/iterable_expand_test.dart
diff --git a/tests/corelib/iterable_expand_test.dart b/tests/corelib/iterable_expand_test.dart
index 5737a9b24cab8305605dcbc02a879f23ab0fe6d1..67aaf5b11624fb25a854b180f7fc34e6fe9e21d8 100644
--- a/tests/corelib/iterable_expand_test.dart
+++ b/tests/corelib/iterable_expand_test.dart
@@ -2,8 +2,6 @@
 // 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() {
   test(expectation, iterable) {
     Expect.listEquals(expectation, iterable.toList());