Devserver: allow SubversionFileSystem to be pinned to a specific rev on construction

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

 # Copyright (c) 2012 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 file_system import FileSystem, StatInfo, FileNotFoundError
 from future import Future
 from object_store_creator import ObjectStoreCreator
 
 class _AsyncUncachedFuture(object):
   def __init__(self,
@@ skipping 95 matching lines @@
 
     if not uncached:
       return Future(value=results)
 
     return Future(delegate=_AsyncUncachedFuture(
         self._file_system.Read(uncached.keys(), binary=binary),
         uncached,
         results,
         self,
         read_object_store))
+
+  def GetIdentity(self):
+    return self._file_system.GetIdentity()