Revert "Remove Expect from core library."

tests/language/div_with_power_of_two_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 division by power of two.
 // Test that results before and after optimization are the same.
 
-import "package:expect/expect.dart";
-
 // [function, [list of tuples argument/result]].
 var expectedResults =
   [ [divBy1,
       [[134217730, 134217730],
        [-134217730, -134217730],
        [10, 10],
        [-10, -10]]],
     [divByNeg1,
       [[134217730, -134217730],
        [-134217730, 134217730],
@@ skipping 77 matching lines @@
         int res = v[1];
         Expect.equals(res, f(arg));
       }
     }
     try {
       divBy0(4);
       Expect.fail("Should have thrown exception.");
     } on IntegerDivisionByZeroException catch (e) {}
   }
 }