Docserver: Update Future.Then() to be more Promise-like

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

 #!/usr/bin/env python
 # 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 FileNotFoundError, StatInfo
 from mock_file_system import MockFileSystem
 from test_file_system import TestFileSystem
 import unittest
@@ skipping 42 matching lines @@
     fs.ReadSingle('extensions/').Get()
     self.assertTrue(*fs.CheckAndReset(read_count=2, read_resolve_count=2))
     self.assertFalse(*fs.CheckAndReset(read_count=2, read_resolve_count=2))
     self.assertTrue(*fs.CheckAndReset())
 
     fs.ReadSingle('404.html').Get()
     self.assertTrue(*fs.CheckAndReset(read_count=1, read_resolve_count=1))
     future = fs.Read(['notfound.html', 'apps/'])
     self.assertTrue(*fs.CheckAndReset(read_count=1))
     self.assertRaises(FileNotFoundError, future.Get)
-    self.assertTrue(*fs.CheckAndReset(read_resolve_count=1))
+    self.assertTrue(*fs.CheckAndReset(read_resolve_count=0))
 
     fs.Stat('404.html')
     fs.Stat('404.html')
     fs.Stat('apps/')
     self.assertFalse(*fs.CheckAndReset(stat_count=42))
     self.assertFalse(*fs.CheckAndReset(stat_count=42))
     self.assertTrue(*fs.CheckAndReset())
 
     fs.ReadSingle('404.html').Get()
     fs.Stat('404.html')
@@ skipping 62 matching lines @@
     self.assertEqual(StatInfo('2'), fs.Stat('apps/fakedir/file.html'))
     self.assertEqual(StatInfo('0', child_versions={
       'activeTab.html': '0',
       'alarms.html': '0'
     }), fs.Stat('extensions/'))
     self.assertEqual('Newer version!', fs.ReadSingle('404.html').Get())
     self.assertEqual('yo', fs.ReadSingle('apps/fakedir/file.html').Get())
 
 if __name__ == '__main__':
   unittest.main()