Revert "Remove Expect from core library."

tests/lib/math/min_max_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.
 // Dart test for testing Math.min and Math.max.
 
 library min_max_test;
-import "package:expect/expect.dart";
 import 'dart:math';
 
 testMin() {
   Expect.equals(0, min(0, 2));
   Expect.equals(0, min(2, 0));
 
   Expect.equals(-10, min(-10, -9));
   Expect.equals(-10, min(-10, 9));
   Expect.equals(-10, min(-10, 0));
   Expect.equals(-10, min(-9, -10));
@@ skipping 498 matching lines @@
   Expect.isTrue(max(-inf, -0.0).isNegative);
   Expect.isTrue(max(-inf, -499).isNegative);
   Expect.isTrue(max(-inf, -499.0).isNegative);
   Expect.isTrue(max(-inf, -inf).isNegative);
 }
 
 main() {
   testMin();
   testMax();
 }