Revert "Remove Expect from core library."

tests/language/constructor_redirect_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 redirection constructors.
 
-import "package:expect/expect.dart";
-
 class A {
   var x;
   A(this.x) {}
   A.named(x, int y) : this(x + y);
   A.named2(int x, int y, z) : this.named(staticFun(x, y), z);
 
   // The following is a bit tricky. It is a compile-time error to
   // refer to this (implicitly or explicitly) from an initializer.
   // When we remove the line with moreStaticFun, staticFun is really a
   // static function and it is legal to call it. This is what will
@@ skipping 45 matching lines @@
     D d = const D(498);
     Expect.equals(499, d.x);
     d = const D.named(249);
     Expect.equals(499, d.x);
   }
 }
 
 main() {
   ConstructorRedirectTest.testMain();
 }