Filter out 'FileSystemException: Failed to watch path' from _PhysicalFolder.changes.

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index 411d0d1a6d9961a54502e8588993cb62c1ec2a8f..b190c1bf9a45cd6946163b89c2f89df94d814597 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -226,7 +226,9 @@ class _PhysicalFolder extends _PhysicalResource implements Folder {
   _PhysicalFolder(io.Directory directory) : super(directory);
 
   @override
-  Stream<WatchEvent> get changes => new DirectoryWatcher(_entry.path).events;
+  Stream<WatchEvent> get changes => new DirectoryWatcher(_entry.path)
+      .events
+      .handleError(() {}, test: (error) => error is io.FileSystemException);
 
   /**
    * Return the underlying file being represented by this wrapper.