Public API changes are allowed if an owner is TBR'ed.

The following TBR formats are supported:
* TBR=reed
* TBR=reed@google.com
* TBR=xyz,reed
* TBR=xyz,reed@google.com

BUG=skia:2870
R=borenet@google.com

Author: rmistry@google.com

Review URL: https://codereview.chromium.org/504843003

PRESUBMIT.py

@@ -20,6 +20,7 @@ REVERT_CL_SUBJECT_PREFIX = 'Revert '
 
 SKIA_TREE_STATUS_URL = 'http://skia-tree-status.appspot.com'
 
+# Please add the complete email address here (and not just 'xyz@' or 'xyz').
 PUBLIC_API_OWNERS = (
     'reed@chromium.org',
     'reed@google.com',
@@ -206,6 +207,16 @@ def _CheckLGTMsForPublicAPI(input_api, output_api):
     if re.match(REVERT_CL_SUBJECT_PREFIX, issue_properties['subject'], re.I):
       # It is a revert CL, ignore the public api owners check.
       return results
+
+    match = re.search(r'^TBR=(.*)$', issue_properties['description'], re.M)
+    if match:
+      tbr_entries = match.group(1).strip().split(',')
+      for owner in PUBLIC_API_OWNERS:
+        if owner in tbr_entries or owner.split('@')[0] in tbr_entries:
+          # If an owner is specified in the TBR= line then ignore the public
+          # api owners check.
+          return results
+
     if issue_properties['owner_email'] in PUBLIC_API_OWNERS:
       # An owner created the CL that is an automatic LGTM.
       lgtm_from_owner = True