Fixing relative paths and adding a docstring

tools-webrtc/gn_check_autofix.py

Index: tools-webrtc/gn_check_autofix.py
diff --git a/tools-webrtc/gn_check_autofix.py b/tools-webrtc/gn_check_autofix.py
index 54ca1b0418621dce102bf9fa572dd87831dc6b75..2a5dc30501e22129c7641cb107a33545626af830 100644
--- a/tools-webrtc/gn_check_autofix.py
+++ b/tools-webrtc/gn_check_autofix.py
@@ -8,6 +8,18 @@
 # 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
@@ -97,9 +109,9 @@ def main():
 
   with TemporaryDirectory() as tmp_dir:
     mb_gen_command = ([
-        'tools/mb/mb.py', 'gen',
+        'tools-webrtc/mb/mb.py', 'gen',

[kjellander_webrtc, 2016/12/20 13:35:55]

I'm a bit curious how this works. Does the script only work when being run from
the src/ directory as current working directory? 

Not that we have to fix that, but usually I use something like SCRIPT_DIR:
https://cs.chromium.org/chromium/src/third_party/webrtc/tools/compare_videos....
then I do os.path.join(SCRIPT_DIR...
to get absolute paths.

[mbonadei, 2016/12/20 13:47:38]

Yep, it works only if it is run from `src`. I agree that this should be
documented or fixed. Let me fix it.

         tmp_dir,
-        '--config-file', 'webrtc/build/mb_config.pyl',
+        '--config-file', 'tools-webrtc/mb/mb_config.pyl',
     ] + sys.argv[1:])
 
   mb_output = Run(mb_gen_command)