Add check formatting script

The script can be set as pre-commit hook to run clang-format
check automatically on every commit.

Change-Id: I05c8e5266ebc773c7949c64d7a885809070a58ec

packager/tools/git/check_formatting.py

@@ -0,0 +1,50 @@
+#!/usr/bin/python
+#
+# Copyright 2017 Google Inc. All rights reserved.
+#
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+"""Presubmit script to check clang format.
+
+Install as pre-commit hook:
+
+    cp packager/tools/git/check_formatting.py .git/hooks/pre-commit
+
+Steps to install clang-format on your system if you don't have it already:
+
+1. Install the standalone clang-format tool:
+
+    Linux: sudo apt-get install clang-format
+    Mac:   brew install clang-format
+
+2. Download git-clang-format from
+   https://llvm.org/svn/llvm-project/cfe/trunk/tools/clang-format/git-clang-format
+
+3. Move the script somewhere in your path, e.g.
+   sudo mv git-clang-format /usr/bin/
+
+4. Make the script executable: sudo chmod +x /usr/bin/git-clang-format.
+
+5. Check it's been picked up by git: git clang-format -h.
+
+6. Try it out with: git clang-format --diff.
+
+"""
+
+import subprocess
+import sys
+
+if __name__ == '__main__':
+  command = ['git', 'clang-format', '--style', 'Chromium']
+  command += sys.argv[1:]
+  output = subprocess.check_output(command + ['--diff'])
+
+  if output not in [
+      'no modified files to format\n', 'clang-format did not modify any files\n'
+  ]:
+    print output, '\n'
+    print 'Code style is not correct. Please run ', ' '.join(command), '\n'
+    sys.exit(1)
+  else:
+    sys.exit(0)