Add an assert to ensure UTF-8 locale when handling file paths.

client/utils/file_path.py

 # Copyright 2013 The Swarming Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0 that
 # can be found in the LICENSE file.
 
 """Provides functions: get_native_path_case(), isabs() and safe_join().
 
 This module assumes that filesystem is not changing while current process
 is running and thus it caches results of functions that depend on FS state.
 """
 
@@ skipping 855 matching lines @@
 
   On Windows, forcibly kills processes that are found to interfere with the
   deletion.
 
   Returns:
     True on normal execution, False if berserk techniques (like killing
     processes) had to be used.
   """
   # Do not assert here yet because this would break too much code.
   root = unicode(root)
+  assert sys.getdefaultencoding() == 'utf-8', sys.getdefaultencoding()
   make_tree_deleteable(root)
   logging.info('rmtree(%s)', root)
 
   # First try the soft way: tries 3 times to delete and sleep a bit in between.
   # Retries help if test subprocesses outlive main process and try to actively
   # use or write to the directory while it is being deleted.
   max_tries = 3
   for i in xrange(max_tries):
     # errors is a list of tuple(function, path, excinfo).
     errors = []
@@ skipping 73 matching lines @@
   errors = []
   shutil.rmtree(root, onerror=lambda *args: errors.append(args))
   if errors:
     # There's no hope.
     sys.stderr.write(
         'Failed to delete %s. The following files remain:\n' % root)
     for _, path, _ in errors:
       sys.stderr.write('- %s\n' % path)
     raise errors[0][2][0], errors[0][2][1], errors[0][2][2]
   return False