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

chrome/common/extensions/docs/server2/instance_servlet.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 appengine_wrappers import IsDevServer
 from branch_utility import BranchUtility
 from caching_file_system import CachingFileSystem
+from empty_dir_file_system import EmptyDirFileSystem
 from github_file_system import GithubFileSystem
 from third_party.json_schema_compiler.memoize import memoize
 from offline_file_system import OfflineFileSystem
 from render_servlet import RenderServlet
 from subversion_file_system import SubversionFileSystem
 from object_store_creator import ObjectStoreCreator
 from server_instance import ServerInstance
 from servlet import Servlet
 
 class _OfflineRenderServletDelegate(RenderServlet.Delegate):
@@ skipping 50 matching lines @@
               GithubFileSystem.Create(object_store_creator))
 
   @staticmethod
   def GetConstructor(delegate_for_test=None):
     render_servlet_delegate = _OfflineRenderServletDelegate(
         delegate_for_test or InstanceServlet.Delegate())
     return lambda request: RenderServlet(request, render_servlet_delegate)
 
   # NOTE: if this were a real Servlet it would implement a Get() method, but
   # GetConstructor returns an appropriate lambda function (Request -> Servlet).