Re-implement directory polling.

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:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 66 matching lines @@
 /// and is polling for changes. If you pass `false` for [waitForReady], it will
 /// not schedule this delay.
 DirectoryWatcher createWatcher({bool waitForReady}) {
   // Use a short delay to make the tests run quickly.
   _watcher = new DirectoryWatcher(_sandboxDir,
       pollingDelay: new Duration(milliseconds: 100));
 
   // Wait until the scan is finished so that we don't miss changes to files
   // that could occur before the scan completes.
   if (waitForReady != false) {
-    schedule(() => _watcher.ready);
+    schedule(() => _watcher.ready, "wait for watcher to be ready");
   }
 
   currentSchedule.onComplete.schedule(() {
     _nextEvent = 0;
     _watcher = null;
   }, "reset watcher");
 
   return _watcher;
 }
 
 void expectEvent(ChangeType type, String path) {
   // Immediately create the future. This ensures we don't register too late and
   // drop the event before we receive it.
   var future = _watcher.events.elementAt(_nextEvent++).then((event) {
     expect(event, new _ChangeMatcher(type, path));
   });
 
   // Make sure the schedule is watching it in case it fails.
   currentSchedule.wrapFuture(future);
 
   // Schedule it so that later file modifications don't occur until after this
   // event is received.
-  schedule(() => future);
+  schedule(() => future, "wait for $type event");
 }
 
 void expectAddEvent(String path) {
   expectEvent(ChangeType.ADD, p.join(_sandboxDir, path));
 }
 
 void expectModifyEvent(String path) {
   expectEvent(ChangeType.MODIFY, p.join(_sandboxDir, path));
 }
 
@@ skipping 21 matching lines @@
     new File(fullPath).writeAsStringSync(contents);
 
     // Manually update the mock modification time for the file.
     if (updateModified) {
       // Make sure we always use the same separator on Windows.
       path = p.normalize(path);
 
       var milliseconds = _mockFileModificationTimes.putIfAbsent(path, () => 0);
       _mockFileModificationTimes[path]++;
     }
-  });
+  }, "write file $path");
 }
 
 /// Schedules deleting a file in the sandbox at [path].
 void deleteFile(String path) {
   schedule(() {
     new File(p.join(_sandboxDir, path)).deleteSync();
-  });
+  }, "delete file $path");
 }
 
 /// Schedules renaming a file in the sandbox from [from] to [to].
 ///
 /// If [contents] is omitted, creates an empty file.
 void renameFile(String from, String to) {
   schedule(() {
     new File(p.join(_sandboxDir, from)).renameSync(p.join(_sandboxDir, to));
 
     // Make sure we always use the same separator on Windows.
     to = p.normalize(to);
 
     // Manually update the mock modification time for the file.
     var milliseconds = _mockFileModificationTimes.putIfAbsent(to, () => 0);
     _mockFileModificationTimes[to]++;
-  });
+  }, "rename file $from to $to");
 }
 
 /// A [Matcher] for [WatchEvent]s.
 class _ChangeMatcher extends Matcher {
   /// The expected change.
   final ChangeType type;
 
   /// The expected path.
   final String path;
 
   _ChangeMatcher(this.type, this.path);
 
   Description describe(Description description) {
     description.add("$type $path");
   }
 
   bool matches(item, Map matchState) =>
       item is WatchEvent &&
       item.type == type &&
       p.normalize(item.path) == p.normalize(path);
 }