Add a note that landmines should not be used in general.

build/get_landmines.py

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 """
 This file emits the list of reasons why a particular build needs to be clobbered
 (or a list of 'landmines').
 """
 
 import sys
 
 import landmine_utils
 
 
 builder = landmine_utils.builder
 distributor = landmine_utils.distributor
 gyp_defines = landmine_utils.gyp_defines
 gyp_msvs_version = landmine_utils.gyp_msvs_version
 platform = landmine_utils.platform
 
 
 def print_landmines():
   """
   ALL LANDMINES ARE EMITTED FROM HERE.
   """
+  # DO NOT add landmines as part of a regular CL. Landmines are a last-effort
+  # bandaid fix if a CL that got landed has a build dependency bug and all bots
+  # need to be cleaned up. If you're writing a new CL that causes build
+  # dependency problems, fix the dependency problems instead of adding a
+  # landmine.
+
   if (distributor() == 'goma' and platform() == 'win32' and
       builder() == 'ninja'):
     print 'Need to clobber winja goma due to backend cwd cache fix.'
   if platform() == 'android':
     print 'Clobber: to handle new way of suppressing findbugs failures.'
     print 'Clobber to fix gyp not rename package name (crbug.com/457038)'
   if platform() == 'win' and builder() == 'ninja':
     print 'Compile on cc_unittests fails due to symbols removed in r185063.'
   if platform() == 'linux' and builder() == 'ninja':
     print 'Builders switching from make to ninja will clobber on this.'
@@ skipping 28 matching lines @@
   print 'Remove NaCl toolchains from the output dir (crbug.com/456902)'
 
 
 def main():
   print_landmines()
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())