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

chrome/common/extensions/docs/server2/chroot_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.
 
 import posixpath
 
 from docs_server_utils import StringIdentity
 from file_system import FileSystem
 from future import Future
 
@@ skipping 14 matching lines @@
 
   def Read(self, paths, skip_not_found=False):
     # Maintain reverse mapping so the result can be mapped to the original
     # paths given (the result from |file_system| will include |root| in the
     # result, which would be wrong).
     prefixed_paths = {}
     def prefix(path):
       prefixed = posixpath.join(self._root, path)
       prefixed_paths[prefixed] = path
       return prefixed
-    future_result = self._file_system.Read(
-        tuple(prefix(path) for path in paths),
-        skip_not_found=skip_not_found)
-    def resolve():
+    def next(results):
       return dict((prefixed_paths[path], content)
-                  for path, content in future_result.Get().iteritems())
-    return Future(callback=resolve)
+                  for path, content in results.iteritems())
+    return self._file_system.Read(tuple(prefix(path) for path in paths),
+                                  skip_not_found-skip_not_found).Then(next)
 
   def Refresh(self):
     return self._file_system.Refresh()
 
   def Stat(self, path):
     return self._file_system.Stat(posixpath.join(self._root, path))
 
   def GetIdentity(self):
     return StringIdentity(
         '%s/%s' % (self._file_system.GetIdentity(), self._root))
 
   def __repr__(self):
     return 'ChrootFileSystem(%s, %s)' % (
             self._root, repr(self._file_system))