Add src-side launcher for checkdeps

This is first step towards establishing an API between src and recipes.
The goal is to convert all Test subclasses from recipes' steps.py
into scripts like this one.

BUG=422235
R=iannucci@chromium.org

Review URL: https://codereview.chromium.org/645593002

Cr-Commit-Position: refs/heads/master@{#299086}

testing/scripts/checkdeps.py

+#!/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.
+
+import argparse
+import contextlib
+import json
+import os
+import subprocess
+import sys
+import tempfile
+
+
+SCRIPT_DIR = os.path.abspath(os.path.dirname(__file__))
+SRC_DIR = os.path.abspath(
+    os.path.join(SCRIPT_DIR, os.path.pardir, os.path.pardir))
+
+
+def run_command(argv):
+  print 'Running %r' % argv
+  rc = subprocess.call(argv)
+  print 'Command %r returned exit code %d' % (argv, rc)
+  return rc
+
+
+@contextlib.contextmanager
+def temporary_file():
+  fd, path = tempfile.mkstemp()
+  os.close(fd)
+  try:
+    yield path
+  finally:
+    os.remove(path)
+
+
+def mode_run(args):
+  with temporary_file() as tempfile_path:
+    rc = run_command([
+        os.path.join(SRC_DIR, 'buildtools', 'checkdeps', 'checkdeps.py'),
+        '--json', tempfile_path
+    ])
+
+    with open(tempfile_path) as f:
+      checkdeps_results = json.load(f)
+
+  result_set = set()
+  for result in checkdeps_results:
+    for violation in result['violations']:
+      result_set.add((result['dependee_path'], violation['include_path']))
+
+  with open(args.output, 'w') as f:
+    json.dump({
+        'valid': True,
+        'failures': ['%s: %s' % (r[0], r[1]) for r in result_set],
+    }, f)
+
+  return rc
+
+
+def main(argv):
+  parser = argparse.ArgumentParser()
+
+  subparsers = parser.add_subparsers()
+
+  run_parser = subparsers.add_parser('run')
+  run_parser.add_argument('--output', required=True)
+  run_parser.set_defaults(func=mode_run)
+
+  args = parser.parse_args(argv)
+  return args.func(args)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))