Make the IPC OWNERS check a warning until landing

PRESUBMIT.py

 # Copyright (c) 2012 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
@@ skipping 1467 matching lines @@
     for pattern, entry in patterns.iteritems():
       missing_lines.extend(entry['rules'])
       files.extend(['  %s' % f.LocalPath() for f in entry['files']])
     if missing_lines:
       errors.append(
           '%s is missing the following lines:\n\n%s\n\nfor changed files:\n%s' %
           (owners_file, '\n'.join(missing_lines), '\n'.join(files)))
 
   results = []
   if errors:
-    results.append(output_api.PresubmitError(
+    if input_api.is_committing:
+      output = output_api.PresubmitError
+    else:
+      output = output_api.PresubmitPromptWarning
+    results.append(output(
         'Found changes to IPC files without a security OWNER!',
         long_text='\n\n'.join(errors)))
 
   return results
 
 
 def _CheckAndroidToastUsage(input_api, output_api):
   """Checks that code uses org.chromium.ui.widget.Toast instead of
      android.widget.Toast (Chromium Toast doesn't force hardware
      acceleration on low-end devices, saving memory).
@@ skipping 715 matching lines @@
   results.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api,
       output_api,
       json_url='http://chromium-status.appspot.com/current?format=json'))
 
   results.extend(input_api.canned_checks.CheckChangeHasBugField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   return results