[Extern Generation] Add a presubmit script to check externs not being updated

extensions/common/api/PRESUBMIT.py

+# Copyright 2016 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.
+
+"""Chromium presubmit script for src/extensions/common.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
+for more details on the presubmit API built into depot_tools.
+"""
+
+import sys
+
+_API_PAIRS = {
+    'extensions/common/api/bluetooth.idl': 'ui/externs/bluetooth.js',

[Devlin, 2016/02/22 23:26:14]

Just adding one for now.
Step 2: add all the ones that already have dedicated extern files.
Step 3-n: add the rest.

[Dan Beam, 2016/02/23 03:15:23]

nit: use os.path.join() maybe?

[Devlin, 2016/02/23 23:12:39]

Good call, done.

+    #TODO(devlin): Add more!
+}
+
+def _CheckExterns(input_api, output_api):
+  original_sys_path = sys.path
+
+  try:
+    sys.path.append(input_api.PresubmitLocalPath())
+    from externs_checker import ExternsChecker
+  finally:
+    sys.path = original_sys_path
+
+  return ExternsChecker(input_api, output_api, _API_PAIRS).RunChecks()
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CheckExterns(input_api, output_api)