tools: add unowned-flags tool

This program generates a list of all the currently unowned flags.

Bug: 897809
Change-Id: Ifc5462557fe16784b792dc4d3811fc447bf566db
Reviewed-on: https://chromium-review.googlesource.com/c/1458598
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629980}

tools/flags/unowned-flags.py

+#!/usr/bin/env python
+# Copyright 2019 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.
+#
+# $ unowned-flags.py chrome/browser/flag-metadata.json
+# This program emits a list of all flags in the metadata file that have no
+# owners entry, or whose owners entry is an empty list.
+
+import os
+import sys
+
+PYJSON5_PATH = os.path.join(os.path.dirname(__file__),
+                            '..', '..', 'third_party', 'pyjson5', 'src')
+sys.path.append(PYJSON5_PATH)
+
+import json5
+
+
+def load_metadata(filename):
+  return json5.load(open(filename))
+
+
+def print_unowned_flags(filename):
+  metadata = load_metadata(filename)
+  for flag in metadata:
+    if not flag.get('owners'):
+      print flag['name']
+
+
+if __name__ == '__main__':
+  print_unowned_flags(sys.argv[1])