Update unittest to new package layout.

tests/isolate/cross_isolate_message_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.
 
 // Dart test program for testing that isolates can communicate to isolates
 // other than the main isolate.
 
 #library('CrossIsolateMessageTest');
 #import('dart:isolate');
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 void crossIsolate1() {
   port.receive((msg, replyTo) {
     SendPort otherIsolate = msg;
     ReceivePort receivePort = new ReceivePort();
     receivePort.receive((msg, replyTo) {
       otherIsolate.send(msg + 58, null);  // 100.
       receivePort.close();
     });
     replyTo.send(['ready', receivePort.toSendPort()]);
@@ skipping 29 matching lines @@
         Expect.equals("ready", msg[0]);
         myPort.receive(expectAsync2((msg, replyTo) {
           Expect.equals(499, msg);
           myPort.close();
         }));
         msg[1].send(42, null);
       }));
     }));
   });
 }