make tests work, implement 'set noparent', owners propagating down

tests/filesystem_mock.py

 #!/usr/bin/python
 # Copyright (c) 2011 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 errno
 import os
 import re
 import StringIO
 
@@ skipping 14 matching lines @@
     self.written_files = {}
     self._sep = '/'
 
   @property
   def sep(self):
     return self._sep
 
   def _split(self, path):
     return path.rsplit(self.sep, 1)
 
+  def abspath(self, path):
+    if path.endswith(self.sep):
+      return path[:-1]
+    return path
+
   def dirname(self, path):
-    if not self.sep in path:
+    if self.sep not in path:
       return ''
-    return self._split(path)[0]
+    return self._split(path)[0] or self.sep
 
   def exists(self, path):
     return self.isfile(path) or self.isdir(path)
 
   def isfile(self, path):
     return path in self.files and self.files[path] is not None
 
   def isdir(self, path):
     if path in self.files:
       return False
     if not path.endswith(self.sep):
       path += self.sep
 
     # We need to use a copy of the keys here in order to avoid switching
     # to a different thread and potentially modifying the dict in
     # mid-iteration.
     files = self.files.keys()[:]
     return any(f.startswith(path) for f in files)
 
   def join(self, *comps):
-    # FIXME: might want tests for this and/or a better comment about how
+    # TODO: Might want tests for this and/or a better comment about how
     # it works.
     return re.sub(re.escape(os.path.sep), self.sep, os.path.join(*comps))
 
   def open_for_reading(self, path):
     return StringIO.StringIO(self.read_binary_file(path))
 
   def read_binary_file(self, path):
     # Intentionally raises KeyError if we don't recognize the path.
     if self.files[path] is None:
       _RaiseNotFound(path)
     return self.files[path]