[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
+
+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
+
+  join = input_api.os_path.join
+  api_root = input_api.PresubmitLocalPath()
+  externs_root = join(
+      input_api.PresubmitLocalPath(), '..', '..', '..', 'ui', 'externs')

[Dan Beam, 2016/02/23 23:26:17]

externs_root = join(api_root, '..', '..', '..', 'ui', 'externs')

[Devlin, 2016/02/24 00:05:05]

Whoops, done.

+
+  api_pairs = {
+    join(api_root, 'bluetooth.idl'): join(externs_root, 'bluetooth.js'),
+    #TODO(devlin): Add more!

[Dan Beam, 2016/02/23 23:26:17]

nit: # TODO(rdevlin.cronin):

[Devlin, 2016/02/24 00:05:05]

I know it's unusual, but I use devlin just about everywhere.  In codesearch,
there's 64 TODO(devlin) and 18 TODO(rdevlin.cronin).  I'd like to stick with
this.

[Dan Beam, 2016/02/24 00:15:31]

you should change TODO(devlin) to TODO(rdevlin.cronin), IMO
http://www.chromium.org/chromium-os/python-style-guidelines#TOC-TODOs
https://google.github.io/styleguide/pyguide.html#TODO_Comments

[Devlin, 2016/02/24 00:24:23]

Changed here.

[Devlin, 2016/02/24 00:27:30]

For reference, the reasons I prefer devlin are:
- searchable internally and externally (devlin is my codereview setting, and
will also show up on internal chat - rdevlin.cronin will not, as my google
username is different).
- shorter.
- more recognizable.
- avoids people calling me rdevlin. :)

Note also that "devlin" works with rdevlin.cronin for things like "git log
--author=devlin".

+  }
+
+  return ExternsChecker(input_api, output_api, api_pairs).RunChecks()
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CheckExterns(input_api, output_api)