Histograms.xml python script housekeeping

tools/metrics/histograms/update_extension_permission.py

 # Copyright 2014 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.
 
 """Updates ExtensionPermission2 and ExtensionPermission3 enums in histograms.xml
 file with values read from permission_message.h and api_permission.h,
 respectively.
 
 If the file was pretty-printed, the updated version is pretty-printed too.
 """
 
 import os
 import sys
 
 from update_histogram_enum import UpdateHistogramEnum
 
 if __name__ == '__main__':
   if len(sys.argv) > 1:
     print >>sys.stderr, 'No arguments expected!'
     sys.stderr.write(__doc__)
     sys.exit(1)
 
+  header_file = 'extensions/common/permissions/permission_message.h'
   UpdateHistogramEnum(histogram_enum_name='ExtensionPermission2',
-                      source_enum_path=os.path.join('..', '..', '..',
-                                                    'extensions', 'common',
-                                                    'permissions',
-                                                    'permission_message.h'),
+                      source_enum_path=header_file,
                       start_marker='^enum ID {',
                       end_marker='^kEnumBoundary')
 
+  header_file = 'extensions/common/permissions/api_permission.h'
   UpdateHistogramEnum(histogram_enum_name='ExtensionPermission3',
-                      source_enum_path=os.path.join('..', '..', '..',
-                                                    'extensions', 'common',
-                                                    'permissions',
-                                                    'api_permission.h'),
+                      source_enum_path=header_file,
                       start_marker='^enum ID {',
                       end_marker='^kEnumBoundary')