Revert "Remove Expect from core library."

tests/language/generic_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.
 // VMOptions=--checked
+//
 // Dart test program testing generic type allocations and generic type tests.
-import "package:expect/expect.dart";
 
 class A {
   const A();
 }
 
 class AA extends A {
   const AA();
 }
 
 class AX {
@@ skipping 53 matching lines @@
 
   static testMain() {
     Expect.equals(1, test());
   }
 }
 
 
 main() {
   GenericTest.testMain();
 }