Wrap Directory.watch on Mac OS for the watcher package.

pkg/watcher/test/utils.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.
 
 library watcher.test.utils;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
@@ skipping 119 matching lines @@
     currentSchedule.onComplete.schedule(() {
       var numEvents = _nextEvent;
       subscription.cancel();
       _nextEvent = 0;
       _watcher = null;
 
       // If there are already errors, don't add this to the output and make
       // people think it might be the root cause.
       if (currentSchedule.errors.isEmpty) {
         expect(allEvents, hasLength(numEvents));
+      } else {
+        currentSchedule.addDebugInfo("Events fired:\n${allEvents.join('\n')}");
       }
     }, "reset watcher");
 
     return _watcher.events;
   }, "create watcher")).asBroadcastStream();
 
   schedule(() => _watcher.ready, "wait for watcher to be ready");
 }
 
 /// A future set by [inAnyOrder] that will complete to the set of events that
@@ skipping 135 matching lines @@
 void withPermutations(callback(int i, int j, int k), {int limit}) {
   if (limit == null) limit = 3;
   for (var i = 0; i < limit; i++) {
     for (var j = 0; j < limit; j++) {
       for (var k = 0; k < limit; k++) {
         callback(i, j, k);
       }
     }
   }
 }