Revert "Remove Expect from core library."

tests/language/named_parameters_aggregated_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.
 // Dart test program for testing named parameters.
 
-import "package:expect/expect.dart";
-
 
 class TypeTester<T> {}
 
 // Expect compile-time error as no default values are allowed
 // in closure type definitions.
 typedef void Callback([String msg
  = ""  /// 01: compile-time error
  ]);
 
 class NamedParametersAggregatedTests {
@@ skipping 31 matching lines @@
   );
 
   // Expect compile-time error due to missing positional argument.
   NamedParametersAggregatedTests.F31(b:25, c:35);  /// 05: static type warning
 
   new TypeTester<Callback>();
 
   (new NamedParametersAggregatedTests()).InstallCallback(null);
 
 }