Revert "Remove Expect from core library."

tests/language/instanceof_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 InstanceofTest {
 
   InstanceofTest() {}
 
   static void testBasicTypes() {
     Expect.equals(true, 0 is int);
     Expect.equals(false, (0 is bool));
     Expect.equals(false, (0 is String));
     Expect.equals(true, 1 is int);
     Expect.equals(false, (1 is bool));
@@ skipping 164 matching lines @@
 
 class D extends C {D() : super() {}}
 
 main() {
   // Repeat type checks so that inlined tests can be tested as well.
   for (int i = 0; i < 5; i++) {
     InstanceofTest.testMain();
   }
 }