Docs: Memoize the FeaturesBundles that are created by AvailabilityFinder to

chrome/common/extensions/docs/server2/features_bundle.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 compiled_file_system import Unicode
+from compiled_file_system import SingleFile, Unicode
 from extensions_paths import (
     API_FEATURES, JSON_TEMPLATES, MANIFEST_FEATURES, PERMISSION_FEATURES)
 import features_utility
 from file_system import FileNotFoundError
 from future import Future
 from third_party.json_schema_compiler.json_parse import Parse
 
 
 def _AddPlatformsFromDependencies(feature,
                                   api_features,
@@ skipping 15 matching lines @@
     # If the dependency can't be resolved, it is inaccessible and therefore
     # so is this feature.
     if dependency_feature is None:
       return []
     platforms = platforms.union(dependency_feature['platforms'])
   feature['platforms'] = list(platforms)
 
 
 class _FeaturesCache(object):
   def __init__(self, file_system, compiled_fs_factory, *json_paths):
-    self._cache = compiled_fs_factory.Create(
-        file_system, self._CreateCache, type(self))
+    populate = self._CreateCache
+    if len(json_paths) == 1:
+      populate = SingleFile(populate)

[not at google - send to devlin, 2014/03/28 17:20:36]

and this is a minor optimisation to stop us from re-download api_features each
cron job unnecessarily. not a big one but I noticed it in passing.

+
+    self._cache = compiled_fs_factory.Create(file_system, populate, type(self))
     self._text_cache = compiled_fs_factory.ForUnicode(file_system)
     self._json_path = json_paths[0]
     self._extra_paths = json_paths[1:]
 
   @Unicode
   def _CreateCache(self, _, features_json):
     extra_path_futures = [self._text_cache.GetFromFile(path)
                           for path in self._extra_paths]
     features = features_utility.Parse(Parse(features_json))
     for path_future in extra_path_futures:
@@ skipping 57 matching lines @@
       # TODO(rockot): Handle inter-API dependencies more gracefully.
       # Not yet a problem because there is only one such case (windows -> tabs).
       # If we don't store this value before annotating platforms, inter-API
       # dependencies will lead to infinite recursion.
       for feature in api_features.itervalues():
         _AddPlatformsFromDependencies(
             feature, api_features, manifest_features, permission_features)
       self._object_store.Set('api_features', api_features)
       return api_features
     return Future(callback=resolve)