Revert "Remove Expect from core library."

tests/language/instance_incr_deopt_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.
 
-import "package:expect/expect.dart";
-
 // Check correct deoptimization of instance field increment.
 
 
 main() {
   var a = new A();
   var aa = new A();
   for (int i = 0; i < 2000; i++) {
     a.Incr();
     myIncr(aa);
     conditionalIncr(false, a);
@@ skipping 30 matching lines @@
     f++;
   }
   var f;
 }
 
 class B {
   B() : f = 0;
   var f;
 }