tools/gn: add python shebang directive to roll_gn script
This way we can execute it from the command line like the following:
$ ./tools/gn/bin/roll_gn.py
Otherwise, on Linux you have to call python directly, like:
$ python ./tools/gn/bin/roll_gn.py
BUG=None
TEST=see above
R=dpranke@chromium.org
TBR=brettw@chromium.org
Review URL: https://codereview.chromium.org/1458603010
Cr-Original-Commit-Position: refs/heads/master@{#360620}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f7bc7c2c72c0d7f9bdb327154845b5baaf9ca72a
diff --git a/tools/gn/bin/roll_gn.py b/tools/gn/bin/roll_gn.py
old mode 100644
new mode 100755
index 66c711a..10b218c
--- a/tools/gn/bin/roll_gn.py
+++ b/tools/gn/bin/roll_gn.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python
# 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.