Revert "Remove Expect from core library."

tests/lib/math/low_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 the default PRNG does uniformly distribute values when not using
 // a power of 2.
 
 // Library tag to allow Dartium to run the test.
 library low_test;
 
-import "package:expect/expect.dart";
 import 'dart:math';
 
 void main() {
   var n = (2 * (1<<32)) ~/ 3;
   var n2 = n ~/ 2;
   
   var iterations = 200000;
 
   var seed = new Random().nextInt(1<<16);
   print("low_test seed: $seed");
   var prng = new Random(seed);
 
   var low = 0;
   for (var i = 0; i < iterations; i++) {
     if (prng.nextInt(n) < n2) {
       low++;
     }
   }
   
   var diff = (low - (iterations ~/ 2)).abs();
   print("$low, $diff");
   Expect.isTrue(diff < (iterations ~/ 20)); 
 }