Revert "Remove Expect from core library."

tests/standalone/status_expression_test.dart

 // Copyright (c) 2011, 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 StatusExpressionTest;
 
-import "package:expect/expect.dart";
 import "../../tools/testing/dart/status_expression.dart";
 
 
 class StatusExpressionTest {
   static void testMain() {
     test1();
     test2();
     test3();
     test4();
     test5();
@@ skipping 123 matching lines @@
     environment["arch"] = "arm";
     Expect.isFalse(ast.evaluate(environment));
     environment["checked"] = true;
     Expect.isFalse(ast.evaluate(environment));
   }
 }
 
 main() {
   StatusExpressionTest.testMain();
 }