find_unmapped_histograms.py command-line typo fix

tools/metrics/histograms/find_unmapped_histograms.py

 # Copyright 2013 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.
 
 """Scans the Chromium source for histograms that are absent from histograms.xml.
 
 This is a heuristic scan, so a clean run of this script does not guarantee that
 all histograms in the Chromium source are properly mapped.  Notably, field
 trials are entirely ignored by this script.
 
@@ skipping 318 matching lines @@
     help='scan within DIRECTORY for histograms [optional, defaults to "%s"]' %
         default_root,
     metavar='DIRECTORY')
   parser.add_option(
     '--histograms-file', dest='histograms_file_location',
     default=default_histograms_path,
     help='read histogram definitions from FILE (relative to --root-directory) '
          '[optional, defaults to "%s"]' % default_histograms_path,
     metavar='FILE')
   parser.add_option(
-    '--exrta_histograms-file', dest='extra_histograms_file_location',
+    '--extra_histograms-file', dest='extra_histograms_file_location',
     default=default_extra_histograms_path,
     help='read additional histogram definitions from FILE (relative to '
          '--root-directory) [optional, defaults to "%s"]' %
          default_extra_histograms_path,
     metavar='FILE')
   parser.add_option(
       '--csv', action='store_true', dest='output_as_csv', default=False,
       help=(
           'output as csv for ease of parsing ' +
           '[optional, defaults to %default]'))
@@ skipping 26 matching lines @@
     logging.warning('No such file: %s', options.extra_histograms_file_location)
 
   if options.output_as_csv:
     output_csv(unmapped_histograms, location_map)
   else:
     output_log(unmapped_histograms, location_map, options.verbose)
 
 
 if __name__ == '__main__':
   main()