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

pkg/analyzer/lib/file_system/physical_file_system.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.file_system.physical_file_system;
 
 import 'dart:async';
 import 'dart:core';
 import 'dart:io' as io;
 
@@ skipping 208 matching lines @@
   }
 }
 
 /**
  * A `dart:io` based implementation of [Folder].
  */
 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.
    */
   io.Directory get _directory => _entry as io.Directory;
 
   @override
   String canonicalizePath(String relPath) {
     return normalize(join(path, relPath));
   }
@@ skipping 173 matching lines @@
           timer.cancel();
         }
       });
       return completer.future;
     }
     _isSpawning = true;
     _runner = await IsolateRunner.spawn();
     return _runner;
   }
 }