Docserver: Further refactoring to the new GithubFileSystem to make it update

chrome/common/extensions/docs/server2/github_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.
 
 import json
 import logging
 import os
 from StringIO import StringIO
 
 import appengine_blobstore as blobstore
@@ skipping 177 matching lines @@
       logging.warning('Github authentication failed for %s, falling back to '
                       'unauthenticated.' % USERNAME)
       try:
         result = self._fetcher.Fetch('commits/HEAD')
       except urlfetch.DownloadError as e:
         logging.warning('GithubFileSystem Stat: %s' % e)
         return self._DefaultStat(path)
 
     # Parse response JSON - but sometimes github gives us invalid JSON.
     try:
-      version = json.loads(result.content)['commit']['tree']['sha']
+      version = json.loads(result.content)['commit']['sha']
       self._stat_object_store.Set(path, version)
       return StatInfo(version)
     except StandardError as e:
       logging.warning(
           ('%s: got invalid or unexpected JSON from github. Response status ' +
            'was %s, content %s') % (e, result.status_code, result.content))
       return self._DefaultStat(path)
 
   def GetIdentity(self):
     return '%s@%s' % (self.__class__.__name__, StringIdentity(self._url))