Revert "Remove Expect from core library."

tests/corelib/int_parse_radix_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.
 
-import "package:expect/expect.dart";
-
 void main() {
   bool checkedMode = false;
   assert(checkedMode = true);
 
   for (int i = 0; i < 36 * 36 + 1; i++) {
     for (int r = 2; r <= 36; r++) {
       String radixString = i.toRadixString(r);
       Expect.equals(i, int.parse(radixString, radix: r), "");
       Expect.equals(i, int.parse(" $radixString", radix: r), "");
       Expect.equals(i, int.parse("$radixString ", radix: r), "");
@@ skipping 64 matching lines @@
   testBadArguments("0", 0);
   testBadArguments("0", 1);
   testBadArguments("0", 37);
 
   // If handleError isn't an unary function, and it's called, it also throws
   // (either TypeError in checked mode, or some failure in unchecked mode).
   Expect.throws(() => int.parse("9", radix: 8, onError: "not a function"));
   Expect.throws(() => int.parse("9", radix: 8, onError: () => 42));
   Expect.throws(() => int.parse("9", radix: 8, onError: (v1, v2) => 42));
 }