Revert "Remove Expect from core library."

tests/language/field_parameter_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 setting/getting of instance fields.
 
-import "package:expect/expect.dart";
-
 class A {
   var x = 4;
   A(this.x);
   A.named([this.x]);
   A.named2([this.x = 2]);
   A.named3();
 }
 
 class B extends A {
   B(x) : super(x + 10);
@@ skipping 12 matching lines @@
   Expect.equals(3, new A.named2(3).x);
   Expect.equals(4, new A.named3().x);
 
   Expect.equals(10, new B(0).x);
   Expect.equals(null, new B.named_().x);
   Expect.equals(11, new B.named(1).x);
   Expect.equals(2, new B.named2_().x);
   Expect.equals(13, new B.named2(3).x);
   Expect.equals(4, new B.named3().x);
 }