Revert "Remove Expect from core library."

tests/language/execute_finally5_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(int param) {
     if (param == 0) {
       try {
         int j;
         j = func();
         try {
@@ skipping 43 matching lines @@
     Expect.equals(1, obj.f1(0));
     Expect.equals(1201, obj.i);
     Expect.equals(4, obj.f1(1));
     Expect.equals(304, obj.i);
   }
 }
 
 main() {
   ExecuteFinally5Test.testMain();
 }