Docserver: there is only one.

chrome/common/extensions/docs/server2/patched_file_system.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from copy import deepcopy
 
 from file_system import FileSystem, StatInfo, FileNotFoundError
 from future import Future
 
 class _AsyncFetchFuture(object):
@@ skipping 138 matching lines @@
       # No changes are made in this directory.
       return self._host_file_system.Stat(path)
 
     if stat_info.child_versions is not None:
       if filename:
         if filename in stat_info.child_versions:
           stat_info = StatInfo(stat_info.child_versions[filename])
         else:
           raise FileNotFoundError('%s was not in child versions' % filename)
     return stat_info
+
+  def GetIdentity(self):
+    return '%s(%s,%s)' % (self.__class__.__name__,
+                          self._host_file_system.GetIdentity(),
+                          self._patcher.GetIdentity())