Stop watching when removing watched path, for Mac OS X as well.

runtime/bin/file_system_watcher_macos.cc

Index: runtime/bin/file_system_watcher_macos.cc
diff --git a/runtime/bin/file_system_watcher_macos.cc b/runtime/bin/file_system_watcher_macos.cc
index de0be2eb9c552fa32aab3fbf8abe894895061709..6d51e9114baedf5771291eeb1ce933e2ab2193ab 100644
--- a/runtime/bin/file_system_watcher_macos.cc
+++ b/runtime/bin/file_system_watcher_macos.cc
@@ -259,6 +259,7 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id) {
     if (bytes < 0) {
       return DartUtils::NewDartOSError();
     }
+    size_t path_len = strlen(e.data.path);
     Dart_Handle event = Dart_NewList(3);
     int flags = e.data.flags;
     int mask = 0;
@@ -266,11 +267,18 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id) {
     if (flags & kFSEventStreamEventFlagItemRenamed) mask |= kMove;
     if (flags & kFSEventStreamEventFlagItemXattrMod) mask |= kModefyAttribute;
     if (flags & kFSEventStreamEventFlagItemCreated) mask |= kCreate;
-    if (flags & kFSEventStreamEventFlagItemRemoved) mask |= kDelete;
+    if (flags & kFSEventStreamEventFlagItemRemoved) {
+      if (path_len == 0) {
+        // The removed path is the path being watched.
+        mask |= kDeleteSelf;
+      } else {
+        mask |= kDelete;
+      }
+    }
     Dart_ListSetAt(event, 0, Dart_NewInteger(mask));
     Dart_ListSetAt(event, 1, Dart_NewInteger(1));
     Dart_ListSetAt(event, 2, Dart_NewStringFromUTF8(
-        reinterpret_cast<uint8_t*>(e.data.path), strlen(e.data.path)));
+        reinterpret_cast<uint8_t*>(e.data.path), path_len));
     Dart_ListSetAt(events, i, event);
   }
   return events;