Revert "Remove Expect from core library."

tests/language/super_operator_index6_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 for unresolved super[].
 
-import "package:expect/expect.dart";
-
 class A {
   var indexField = new List(2);
   operator[]=(index, value) { indexField[index] = value; }
 
   noSuchMethod(InvocationMirror im) {
     if (im.memberName == '[]') {
       Expect.equals(1, im.positionalArguments.length);
       return indexField[im.positionalArguments[0]];
     } else {
       Expect.fail('Should not reach here');
@@ skipping 15 matching lines @@
     Expect.equals(3, super[0] += 1);
     Expect.equals(3, super[0]);
     Expect.equals(3, super[0]++);
     Expect.equals(4, super[0]);
   }
 }
 
 main() {
   new B().test();
 }