Revert "Remove Expect from core library."

tests/language/execute_finally3_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 for testing execution of finally blocks on
 // control flow breaks because of 'return', 'continue' etc.
 
-import "package:expect/expect.dart";
-
 
 class Helper {
   Helper() : i = 0 { }
 
   int f1() {
     try {
       try {
         int j;
         j = func();
         L1:
@@ skipping 46 matching lines @@
   static testMain() {
     Helper obj = new Helper();
     Expect.equals(1401, obj.f1());
     Expect.equals(3001, obj.i);
   }
 }
 
 main() {
   ExecuteFinally3Test.testMain();
 }