Actually make use of the may_prompt flag.

presubmit_support.py

 #!/usr/bin/python
 # Copyright (c) 2006-2009 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.
 
 """Enables directory-specific presubmit checks to run at upload and/or commit.
 """
 
 __version__ = '1.3.2'
 
@@ skipping 749 matching lines @@
   for name, items in (('Messages', notifications),
                       ('Warnings', warnings),
                       ('ERRORS', errors)):
     if items:
       output_stream.write('** Presubmit %s **\n' % name)
       for item in items:
         if not item._Handle(output_stream, input_stream,
                             may_prompt=False):
           error_count += 1
         output_stream.write('\n')
-  if not errors and warnings:
+  if not errors and warnings and may_prompt:
     output_stream.write(
       'There were presubmit warnings. Sure you want to continue? (y/N): ')
     response = input_stream.readline()
     if response.strip().lower() != 'y':
       error_count += 1
   return (error_count == 0)
 
 
 def ScanSubDirs(mask, recursive):
   if not recursive:
@@ skipping 33 matching lines @@
                                options.commit,
                                options.verbose,
                                sys.stdout,
                                sys.stdin,
                                None,
                                False)
 
 
 if __name__ == '__main__':
   sys.exit(Main(sys.argv))