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

pkg/watcher/test/directory_watcher/shared.dart

Index: pkg/watcher/test/directory_watcher/shared.dart
diff --git a/pkg/watcher/test/directory_watcher/shared.dart b/pkg/watcher/test/directory_watcher/shared.dart
index eed606931c5804b7f5ffa0a705ee998c30dcef5a..34b5e6284d3b872a32ef519b46b7b0c82a80fd4d 100644
--- a/pkg/watcher/test/directory_watcher/shared.dart
+++ b/pkg/watcher/test/directory_watcher/shared.dart
@@ -6,6 +6,8 @@ import 'package:scheduled_test/scheduled_test.dart';
 
 import '../utils.dart';
 
+import 'dart:async';
+
 sharedTests() {
   test('does not notify for files that already exist when started', () {
     // Make some pre-existing files.
@@ -218,5 +220,21 @@ sharedTests() {
         });
       });
     });
+
+    test("emits events for many files added at once in a subdirectory with the "
+        "same name as a removed file", () {
+      writeFile("dir/sub");
+      withPermutations((i, j, k) =>
+          writeFile("old/sub-$i/sub-$j/file-$k.txt"));
+      startWatcher(dir: "dir");
+
+      deleteFile("dir/sub");
+      renameDir("old", "dir/sub");
+      inAnyOrder(() {
+        expectRemoveEvent("dir/sub");
+        withPermutations((i, j, k)  =>
+            expectAddEvent("dir/sub/sub-$i/sub-$j/file-$k.txt"));
+      });
+    });
   });
 }