Reland Implement owners check in presubmit for Gerrit.

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index 9bf60ea29f60e404dc7465255c80b84159deae58..bf949133c959efd8552fd8fe1752b34f55a88aaf 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1317,7 +1317,8 @@ class Changelist(object):
       return presubmit_support.DoPresubmitChecks(change, committing,
           verbose=verbose, output_stream=sys.stdout, input_stream=sys.stdin,
           default_presubmit=None, may_prompt=may_prompt,
-          rietveld_obj=self._codereview_impl.GetRieveldObjForPresubmit())
+          rietveld_obj=self._codereview_impl.GetRieveldObjForPresubmit(),
+          gerrit_obj=self._codereview_impl.GetGerritObjForPresubmit())
     except presubmit_support.PresubmitFailure, e:
       DieWithError(
           ('%s\nMaybe your depot_tools is out of date?\n'
@@ -1501,6 +1502,10 @@ class _ChangelistCodereviewBase(object):
     # For non-Rietveld codereviews, this probably should return a dummy object.
     raise NotImplementedError()
 
+  def GetGerritObjForPresubmit(self):
+    # None is valid return value, otherwise presubmit_support.GerritAccessor.
+    return None
+
   def UpdateDescriptionRemote(self, description):
     """Update the description on codereview site."""
     raise NotImplementedError()
@@ -2107,6 +2112,9 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
         raise NotImplementedError()
     return ThisIsNotRietveldIssue()
 
+  def GetGerritObjForPresubmit(self):
+    return presubmit_support.GerritAccessor(self._GetGerritHost())
+
   def GetStatus(self):
     """Apply a rough heuristic to give a simple summary of an issue's review
     or CQ status, assuming adherence to a common workflow.