Revert "Remove Expect from core library."

tests/corelib/list_get_range_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";
-
 main() {
   Expect.listEquals([], [].getRange(0, 0));
   Expect.listEquals([], const [].getRange(0, 0));
 
   Expect.listEquals([], [].getRange(-1, 0));
   Expect.listEquals([], const [].getRange(-1, 0));
 
   Expect.listEquals([1, 2], [1, 2].getRange(0, 2));
   Expect.listEquals([1, 2], const [1, 2].getRange(0, 2));
 
@@ skipping 21 matching lines @@
   expectIOORE(() => [1].getRange(1, 1));
 }
 
 void expectIOORE(Function f) {
   Expect.throws(f, (e) => e is RangeError);
 }
 
 void expectIAE(Function f) {
   Expect.throws(f, (e) => e is ArgumentError);
 }