Revert "Remove Expect from core library."

tests/language/inst_field_initializer_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.
 // Test for instance field initializer expressions.
 
-import "package:expect/expect.dart";
-
 class Cheese {
   static const mild = 1;
   static const stinky = 2;
 
   // Instance fields with initializer expression.
   String name = "";
   var smell = mild;
 
   Cheese() {
     Expect.equals("", this.name);
@@ skipping 35 matching lines @@
   Expect.equals("Munster", munster.name);
   Expect.equals(Cheese.stinky, munster.smell);
 
   var brie = new Cheese.hideAndSeek("Brie");
   Expect.equals("Brie", brie.name);
   Expect.equals(Cheese.mild, brie.smell);
 
   var t = new HasNoExplicitConstructor();
   Expect.equals("Tilsiter", t.s);
 }