Add more python 2.5 compatibility.

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
 
+
 def _RaiseNotFound(path):
   raise IOError(errno.ENOENT, path, os.strerror(errno.ENOENT))
 
 
 class MockFileSystem(object):
   """Stripped-down version of WebKit's webkitpy.common.system.filesystem_mock
 
   Implements a filesystem-like interface on top of a dict of filenames ->
   file contents. A file content value of None indicates that the file should
   not exist (IOError will be raised if it is opened;
@@ skipping 45 matching lines @@
     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]