Revert "Remove Expect from core library."

tests/language/local_function3_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.
 // Dart test program testing closures.
 
-import "package:expect/expect.dart";
-
 class LocalFunction3Test {
   static testExceptions() {
     var f = (int n) { return n + 1; };
     Expect.equals(true, f is Object);
     bool exception_caught = false;
     try {
       f.xyz(0);
     } on NoSuchMethodError catch (e) {
       exception_caught = true;
     }
@@ skipping 11 matching lines @@
 
   static testMain() {
     testExceptions();
   }
 }
 
 main() {
   LocalFunction3Test.testMain();
 }