Revert "Remove Expect from core library."

tests/language/finally_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.
 
-import "package:expect/expect.dart";
-
 // Test for a bug in dart2js where the update of a field in a try
 // block would not be seen by the finally block. See dartbug.com/5517.
 
 class A {
   int i;
   A() : i = 42;
 
   foo() {
     bool executedFinally = false;
     if (i == 42) {
       try {
         i = 12;
       } finally {
         Expect.equals(12, i);
         executedFinally = true;
       }
     }
     Expect.isTrue(executedFinally);
   }
 }
 
 main() {
   new A().foo();
 }