Add presubmit explaining embedding translations in shared UI code

ui/webui/resources/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.
 
 import re
 
 
 def PostUploadHook(cl, change, output_api):
   rietveld_obj = cl.RpcServer()
   description = rietveld_obj.get_description(cl.issue)
 
   existing_bots = (change.CQ_INCLUDE_TRYBOTS or '').split(';')
   clean_bots = set(filter(None, map(lambda s: s.strip(), existing_bots)))
   new_bots = clean_bots | set(
       ['master.tryserver.chromium.linux:closure_compilation'])
   new_tag = 'CQ_INCLUDE_TRYBOTS=%s' % ';'.join(new_bots)
 
   if clean_bots:
     tag_reg = '^CQ_INCLUDE_TRYBOTS=.*$'
     new_description = re.sub(tag_reg, new_tag, description, flags=re.M | re.I)
   else:
     new_description = description + '\n' + new_tag
 
   if new_description == description:
     return []
 
   rietveld_obj.update_description(cl.issue, new_description)
   return [output_api.PresubmitNotifyResult(
       'Automatically added optional Closure bots to run on CQ.')]
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CheckForTranslations(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return _CheckForTranslations(input_api, output_api)
+
+
+def _CheckForTranslations(input_api, output_api):
+  shared_keywords = ['i18n(']
+  html_keywords = shared_keywords + ['$118n{']
+  js_keywords = shared_keywords + ['I18nBehavior', 'loadTimeData.']
+
+  errors = []
+
+  for f in input_api.AffectedFiles():
+    local_path = f.LocalPath()
+
+    keywords = None
+    if local_path.endswith('.js'):
+      keywords = js_keywords
+    elif local_path.endswith('.html'):
+      keywords = html_keywords
+
+    if not keywords:
+      continue
+
+    for lnum, line in f.ChangedContents():
+      if any(line for keyword in keywords if keyword in line):
+        errors.append("%s:%d\n%s" % (f.LocalPath(), lnum, line))
+
+  if not errors:
+    return []
+
+  return [output_api.PresubmitError("\n".join(errors) + """
+
+Don't embed translations directly in shared UI code. Instead, inject your
+translation from the place using the shared code. For an example: see
+<cr-dialog>#closeText (http://bit.ly/2eLEsqh).""")]