Fixing relative paths and adding a docstring

tools-webrtc/gn_check_autofix.py

 #!/usr/bin/env python
 
 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""
+This tool tries to fix (some) errors reported by `gn gen --check` or
+`gn check`.
+It will run `mb gen` in a temporary directory and it is really useful to
+check for different configurations.
+
+Usage:
+    $ python tools-webrtc/gn_check_autofix.py -m some_mater -b some_bot
+    or
+    $ python tools-webrtc/gn_check_autofix.py -c some_mb_config
+"""
+
 import os
 import re
 import shutil
 import subprocess
 import sys
 import tempfile
 
 from collections import defaultdict
 
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+
 TARGET_RE = re.compile(
     r'(?P<indentation_level>\s*)\w*\("(?P<target_name>\w*)"\) {$')
 
 class TemporaryDirectory(object):
   def __init__(self):
     self._closed = False
     self._name = None
     self._name = tempfile.mkdtemp()
 
   def __enter__(self):
@@ skipping 59 matching lines @@
   base_path = base_path[first_difference:]
   dependency_path = dependency_path[first_difference:]
   return (os.path.sep.join((['..'] * len(base_path)) + dependency_path) +
           ':' + dependency)
 
 def main():
   deleted_sources = set()
   errors_by_file = defaultdict(lambda: defaultdict(set))
 
   with TemporaryDirectory() as tmp_dir:
+    mb_script_path = os.path.join(SCRIPT_DIR, 'mb', 'mb.py')
+    mb_config_file_path = os.path.join(SCRIPT_DIR, 'mb', 'mb_config.pyl')
     mb_gen_command = ([
-        'tools/mb/mb.py', 'gen',
+        mb_script_path, 'gen',
         tmp_dir,
-        '--config-file', 'webrtc/build/mb_config.pyl',
+        '--config-file', mb_config_file_path,
     ] + sys.argv[1:])
 
   mb_output = Run(mb_gen_command)
   errors = mb_output[0].split('ERROR')[1:]
 
   if mb_output[1]:
     print mb_output[1]
     return 1
 
   for error in errors:
@@ skipping 20 matching lines @@
       print '\n'.join(error)
       continue
 
   for path, missing_deps in errors_by_file.items():
     FixErrors(path, missing_deps, deleted_sources)
 
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())