Docserver: Pull knowledge of host file systems into a single

chrome/common/extensions/docs/server2/host_file_system_iterator.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 third_party.json_schema_compiler.memoize import memoize
 
 
 class HostFileSystemIterator(object):
   '''Provides methods for iterating through host file systems, in both
   ascending (oldest to newest version) and descending order.
   '''
 
-  def __init__(self, file_system_creator, host_file_system, branch_utility):
-    self._file_system_creator = file_system_creator
-    self._host_file_system = host_file_system
+  def __init__(self, file_system_provider, branch_utility):
+    self._file_system_provider = file_system_provider
     self._branch_utility = branch_utility
 
   @memoize
   def _GetFileSystem(self, branch):
     '''To avoid overwriting the persistent data store entry for the 'trunk'
     host file system, hold on to a reference of this file system and return it
     instead of creating a file system for 'trunk'.
       Also of note: File systems are going to be iterated over multiple times
     at each call of ForEach, but the data isn't going to change between calls.
     Use |branch| to memoize the created file systems.
     '''
-    if branch == 'trunk':
-      # Don't create a new file system for trunk, since there is a bug with the
-      # current architecture and design of HostFileSystemCreator, where
-      # creating 'trunk' ignores the pinned revision (in fact, it bypasses
-      # every difference including whether the file system is patched).
-      # TODO(kalman): Fix HostFileSystemCreator and update this comment.
-      return self._host_file_system
-    return self._file_system_creator.Create(branch)
+    return (self._file_system_provider.GetTrunk() if branch == 'trunk' else
+            self._file_system_provider.GetBranch(branch))
 
   def _ForEach(self, channel_info, callback, get_next):
     '''Iterates through a sequence of file systems defined by |get_next| until
     |callback| returns False, or until the end of the sequence of file systems
     is reached. Returns the BranchUtility.ChannelInfo of the last file system
     for which |callback| returned True.
     '''
     last_true = None
     while channel_info is not None:
       file_system = self._GetFileSystem(channel_info.branch)
       if not callback(file_system, channel_info):
         return last_true
       last_true = channel_info
       channel_info = get_next(channel_info)
     return last_true
 
   def Ascending(self, channel_info, callback):
     return self._ForEach(channel_info, callback, self._branch_utility.Newer)
 
   def Descending(self, channel_info, callback):
     return self._ForEach(channel_info, callback, self._branch_utility.Older)