Revert "Remove Expect from core library."

tests/language/generic2_test.dart

 // Copyright (c) 2013, 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 is-tests with type variables.
 
-import "package:expect/expect.dart";
-
 class A<T> {
   foo(o) => o is T;
 }
 
 class B {}
 
 class C extends A<int> {}
 
 main() {
   Expect.isTrue(new A<Object>().foo(new B()));
   Expect.isTrue(new A<Object>().foo(1));
   Expect.isFalse(new A<int>().foo(new Object()));
   Expect.isFalse(new A<int>().foo('hest'));
   Expect.isTrue(new A<B>().foo(new B()));
   Expect.isFalse(new A<B>().foo(new Object()));
   Expect.isFalse(new A<B>().foo(1));
   Expect.isTrue(new C().foo(1));
   Expect.isFalse(new C().foo(new Object()));
   Expect.isFalse(new C().foo('hest'));
   Expect.isTrue(new A<List<int>>().foo(new List<int>()));
   Expect.isFalse(new A<List<int>>().foo(new List<String>()));
 }