Revert "Remove Expect from core library."

tests/lib/crypto/base64_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.
 
 // Library tag to allow the test to run on Dartium.
 library base64_test;
 
-import "package:expect/expect.dart";
 import 'dart:crypto';
 
 // Data from http://tools.ietf.org/html/rfc4648.
 var inputs =
     const [ '', 'f', 'fo', 'foo', 'foob', 'fooba', 'foobar' ];
 var results =
     const [ '', 'Zg==', 'Zm8=', 'Zm9v', 'Zm9vYg==', 'Zm9vYmE=', 'Zm9vYmFy' ];
 
 var longLine =
     "Man is distinguished, not only by his reason, but by this singular "
@@ skipping 28 matching lines @@
 void main() {
   for (var i = 0; i < inputs.length; i++) {
     var enc = CryptoUtils.bytesToBase64(inputs[i].codeUnits);
     Expect.equals(results[i], enc);
   }
   Expect.equals(CryptoUtils.bytesToBase64(longLine.codeUnits, 76),
                 longLineResult);
   Expect.equals(CryptoUtils.bytesToBase64(longLine.codeUnits),
                 longLineResultNoBreak);
 }