Revert "Remove Expect from core library."

tests/language/named_parameters_passing_null_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";
-
 // Dart test program for testing named parameters with 'null' passed as an
 // argument.
 
 
 class TestClass {
   TestClass();
 
   num method([value = 100]) => value;
   num method2({value: 100}) => value;
 
@@ skipping 22 matching lines @@
   Expect.equals(null, TestClass.staticMethod(null));
   Expect.equals(null, TestClass.staticMethod2(value: null));
 
   Expect.equals(300, globalMethod());
   Expect.equals(300, globalMethod2());
   Expect.equals(50, globalMethod(50));
   Expect.equals(50, globalMethod2(value: 50));
   Expect.equals(null, globalMethod(null));
   Expect.equals(null, globalMethod2(value: null));
 }