Adapt streams for additional stackTrace argument.

pkg/watcher/lib/src/directory_watcher.dart

Index: pkg/watcher/lib/src/directory_watcher.dart
diff --git a/pkg/watcher/lib/src/directory_watcher.dart b/pkg/watcher/lib/src/directory_watcher.dart
index 16a5cf1c502d329041b25dca26ecefeb8254beca..3b39f5a3eaad4c3afda42caa1006afa9694cd3c9 100644
--- a/pkg/watcher/lib/src/directory_watcher.dart
+++ b/pkg/watcher/lib/src/directory_watcher.dart
@@ -133,11 +133,11 @@ class DirectoryWatcher {
 
       if (entity is! File) return;
       _filesToProcess.add(entity.path);
-    }, onError: (error) {
+    }, onError: (error, StackTrace stackTrace) {
       if (!isDirectoryNotFoundException(error)) {
         // It's some unknown error. Pipe it over to the event stream so the
         // user can see it.
-        _events.addError(error);
+        _events.addError(error, stackTrace);
       }
 
       // When an error occurs, we end the listing normally, which has the