Revert "Remove Expect from core library."

tests/language/named_parameters2_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.
 // Dart test program for testing named parameters.
 // You may not provide the same parameter as both a positional and a named argument.
 
-import "package:expect/expect.dart";
-
 int test(int a, [int b]) {
   return a;
 }
 
 main() {
   bool foundError = false;
   try {
     // Parameter b passed twice, as positional and named.
     test(10, 25, b: 26);  /// static type warning
   } on NoSuchMethodError catch (e) {
     foundError = true;
   }
   Expect.equals(true, foundError);
 }