Avoid race in _FileSystemWatcher if subscription closed while event queued.

runtime/bin/file_patch.dart

Index: runtime/bin/file_patch.dart
diff --git a/runtime/bin/file_patch.dart b/runtime/bin/file_patch.dart
index 14499af5182ed9afa940d6d1f35bef278f75870e..479bb9f26c87bade20c6397dcffdc33a6e478a34 100644
--- a/runtime/bin/file_patch.dart
+++ b/runtime/bin/file_patch.dart
@@ -193,6 +193,10 @@ patch class _FileSystemWatcher {
             if (event == null) continue;
             eventCount++;
             int pathId = event[4];
+            if (!_idMap.containsKey(pathId)) {

[Søren Gjesse, 2015/03/13 12:18:00]

I am not sure this is 100% safe, but I have not scrutinized the code.

The pathId is something returned from an OS call (on Linux that is returned from
inotify_add_watch). This id can be reused, so if unwatching something and then
watching something new the OS can reuse the id.

Can this result in events for the first registration being reported on the new
one?

+              // Path is no longer being wathed.
+              continue;
+            }
             bool isDir = getIsDir(event);
             var path = getPath(event);
             if ((event[0] & FileSystemEvent.CREATE) != 0) {