Whitelist chromite/third_party/poster. It's MIT licensed.

tools/checklicenses/checklicenses.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Makes sure that all files contain proper licensing information."""
 
 
 import optparse
 import os.path
@@ skipping 139 matching lines @@
     'third_party/angle': [
         'UNKNOWN',
     ],
 
     # http://crbug.com/222828
     # http://bugs.python.org/issue17514
     'third_party/chromite/third_party/argparse.py': [
         'UNKNOWN',
     ],
 
+    # http://crbug.com/326117
+    # https://bitbucket.org/chrisatlee/poster/issue/21
+    'third_party/chromite/third_party/poster': [
+        'UNKNOWN',
+    ],
+
     # Not used. http://crbug.com/156020
     # Using third_party/cros_dbus_cplusplus/cros_dbus_cplusplus.gyp instead.
     'third_party/cros_dbus_cplusplus/source/autogen.sh': [
         'UNKNOWN',
     ],
     # Included in the source tree but not built. http://crbug.com/156020
     'third_party/cros_dbus_cplusplus/source/examples': [
         'UNKNOWN',
     ],
     'third_party/devscripts': [
@@ skipping 321 matching lines @@
   option_parser.add_option('--ignore-suppressions',
                            action='store_true',
                            default=False,
                            help='Ignore path-specific license whitelist.')
   options, args = option_parser.parse_args()
   return check_licenses(options, args)
 
 
 if '__main__' == __name__:
   sys.exit(main())