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

client/tests/run_isolated_smoke_test.py

 #!/usr/bin/env python
 # Copyright 2012 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.
 
 import json
 import logging
 import os
 import subprocess
 import sys
 import unittest
 
 ROOT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, ROOT_DIR)
 
 import isolated_format
 import run_isolated
+from depot_tools import fix_encoding
 from utils import file_path
 
 import isolateserver_mock
 import test_utils
 
 
 CONTENTS = {
   'check_files.py': """if True:
       import os, sys
       ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
@@ skipping 311 matching lines @@
     # Test that an entry with an invalid file content but same size is NOT
     # detected property.
     cached_file_path = self._test_corruption_common(
         CONTENTS['file1.txt'][:-1] + ' ')
     # TODO(maruel): This corruption is NOT detected.
     # This needs to be fixed.
     self.assertNotEqual(CONTENTS['file1.txt'], read_content(cached_file_path))
 
 
 if __name__ == '__main__':
+  fix_encoding.fix_encoding()
   test_utils.main()