Revert "Remove Expect from core library."

tests/language/load_to_load_forwarding_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 correctness of side effects tracking used by load to load forwarding.
 
-import "package:expect/expect.dart";
-
 class A {
   var x, y;
   A(this.x, this.y);
 }
 
 foo(a) {
   var value1 = a.x;
   var value2 = a.y;
   for (var j = 1; j < 4; j++) {
     value1 |= a.x << (j * 8);
@@ skipping 17 matching lines @@
   return [value1, value2];
 }
 
 main() {
   for (var i = 0; i < 2000; i++) {
     Expect.listEquals([0x02010000, 0x03020100], foo(new A(0, 0)));
     Expect.listEquals([0x02010000, 0x03020100], bar(new A(0, 0), false));
     Expect.listEquals([0x04020000, 0x03020100], bar(new A(0, 0), true));
   }
 }