Revert "Remove Expect from core library."

tests/standalone/io/file_non_ascii_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";
 import 'dart:io';
 import 'dart:isolate';
 
 main() {
   ReceivePort port = new ReceivePort();
 
   // On MacOS you get the decomposed utf8 form of file and directory
   // names from the system. Therefore, we have to check for both here.
   var precomposed = 'æøå';
   var decomposed = new String.fromCharCodes([47, 230, 248, 97, 778]);
@@ skipping 31 matching lines @@
             });
           });
         });
       });
     });
   }).catchError((e) {
     port.close();
     Expect.fail("File not found");
   });
 }