old_contents: #!/usr/bin/env python
  
  import sys
  from lib2to3.main import main
  
  sys.exit(main("custom_fixers"))
  
new_contents: #!/usr/bin/env python
  # Usage is like 2to3:
  # $ maint/scripts/run_fixers.py -wn --no-diffs tornado
  
  import sys
  from lib2to3.main import main
  
  sys.exit(main("custom_fixers"))
  
subject: Add usage comement to run_fixers.py.