Revert "Remove Expect from core library."

tests/language/parameter_initializer_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.
 
-import "package:expect/expect.dart";
-
 class ParameterInitializerTest {
 
   static testMain() {
     var obj = new Foo.untyped(1);
     Expect.equals(1, obj.x);
 
     obj = new Foo.supertype(9);
     Expect.equals(9, obj.x);
 
     obj = new Foo.subtype(7);
@@ skipping 59 matching lines @@
     Expect.equals(x_, 1);
 
     // There is no way to get to the field in Foo.
     Expect.equals(super.x, 1);
   }
 }
 
 main() {
   ParameterInitializerTest.testMain();
 }