Revert "Remove Expect from core library."

tests/language/generic_parameterized_extends_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.
 //
 // Test verifying that generic extends are processed correctly.
 
-import "package:expect/expect.dart";
-
 class A<T> {}
 class B<T1, T2 extends A<T1>> {}
 class C<T1 extends A<T2>, T2> {}
 
 main() {
   var a = new A<String>();
   var b = new B<String, A<String>>();
   var c = new C<A<String>, String>();
   Expect.isTrue(a is Object);
   Expect.isTrue(a is A<Object>);
   Expect.isTrue(a is A<String>);
   Expect.isTrue(a is !A<int>);
   Expect.isTrue(b is Object);
   Expect.isTrue(b is B<Object, A<Object>>);
   Expect.isTrue(b is B<String, A<String>>);
   Expect.isTrue(b is !B<int, A<int>>);
   Expect.isTrue(c is Object);
   Expect.isTrue(c is C<A<Object>, Object>);
   Expect.isTrue(c is C<A<String>, String>);
   Expect.isTrue(c is !C<A<int>, int>);
 }