Revert "Remove Expect from core library."

tests/lib/math/coin_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.
 
 // Test that a coin toss with Random.nextBool() is fair.
 
 // Library tag to allow Dartium to run the test.
 library coin_test;
 
-import "package:expect/expect.dart";
 import 'dart:math';
 
 main() {
   var seed = new Random().nextInt(1<<16);
   print("coin_test seed: $seed");
   var rnd = new Random(seed);
   var heads = 0;
   var tails = 0;
   for (var i = 0; i < 10000; i++) {
     if (rnd.nextBool()) {
       heads++;
     } else {
       tails++;
     }
   }
   print("Heads: $heads\n"
         "Tails: $tails\n"
         "Ratio: ${heads/tails}\n");
   Expect.approxEquals(1.0, heads/tails, 0.1);
 }