refactor presubmit parsing code from git-cl into presubmit

presubmit_canned_checks.py

 # Copyright (c) 2010 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.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 ### Description checks
 
 def CheckChangeHasTestField(input_api, output_api):
   """Requires that the changelist have a TEST= field."""
@@ skipping 630 matching lines @@
     approvers = _Approvers(input_api, owners_db.email_regexp)
     missing_files = owners_db.files_not_covered_by(affected_files, approvers)
     if missing_files:
       return [output_api.PresubmitError('Missing LGTM from an OWNER for: %s' %
               ','.join(missing_files))]
     return []
   elif input_api.change.tags.get('R'):
     return []
 
   suggested_reviewers = owners_db.reviewers_for(affected_files)
-  return [output_api.PresubmitAddText('R=%s' % ','.join(suggested_reviewers))]
+  return [output_api.PresubmitAddReviewers(suggested_reviewers)]
 
 
 def _Approvers(input_api, email_regexp):
   if not input_api.change.issue:
     return []
 
   path = '/api/%s?messages=true'
   url = (input_api.host_url + path) % input_api.change.issue
 
   f = input_api.urllib2.urlopen(url)
   issue_props = input_api.json.load(f)
   owner = input_api.re.escape(issue_props['owner'])
 
   # TODO(dpranke): This mimics the logic in
   # /tools/commit-queue/verifiers/reviewer_lgtm.py
   # We should share the code and/or remove the check there where it is
   # redundant (since the commit queue also enforces the presubmit checks).
   def match_reviewer(r):
     return email_regexp.match(r) and not input_api.re.match(owner, r)
 
   approvers = []
   for m in issue_props.get('messages', []):
     if 'lgtm' in m['text'].lower() and match_reviewer(m['sender']):
       approvers.append(m['sender'])
   return set(approvers)