Revert "Remove Expect from core library."

tests/language/factory_type_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.
 
-import "package:expect/expect.dart";
-
 class A<T> {
   factory A.factory() {
     return new B<T>();
   }
 
   A();
 
   build() {
     return new A<T>();
   }
@@ skipping 18 matching lines @@
 
   Expect.isTrue(new A<List>().build() is A<List>);
   Expect.isFalse(new A<List>().build() is A<Set>);
 
   Expect.isTrue(new A<List>.factory().build() is B<List>);
   Expect.isFalse(new A<List>.factory().build() is B<Set>);
 
   Expect.isTrue(new B<List>().build() is B<List>);
   Expect.isFalse(new B<List>().build() is B<Set>);
 }