Revert "Remove Expect from core library."

tests/language/constructor_body_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 constructors without function bodies.
 
-import "package:expect/expect.dart";
-
 // Test a non-const constructor works without a body.
 class First {
   First(int this.value);
   First.named(int this.value);
   int value;
 }
 
 // Test a const constructor works without a body.
 class Second {
   const Second(int this.value);
   const Second.named(int this.value);
   final int value;
 }
 
 class ConstructorBodyTest {
   static testMain() {
     Expect.equals(4, new First(4).value);
     Expect.equals(5, new First.named(5).value);
     Expect.equals(6, new Second(6).value);
     Expect.equals(7, new Second.named(7).value);
   }
 }
 
 main() {
   ConstructorBodyTest.testMain();
 }