Revert "Remove Expect from core library."

tests/language/generics_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 for generic types.
 
-import "package:expect/expect.dart";
-
 class GenericsTest<T,V> implements Map<int, int> {
   static int myFunc(bool a, bool b) {
     Expect.equals(true, a);
     Expect.equals(false, b);
     return 42;
   }
 
   static void testMain() {
     int a = 1;
     int b = 2;
@@ skipping 34 matching lines @@
         LongGeneric<
             C,
             List<E>,
             Map<G, LongGeneric<I, J, List<A>>>>> id2;
   }
 }
 
 main() {
   GenericsTest.testMain();
 }