Fix failure in printing/BUILD.gn when not using a sysroot. Without this change, gn gen fails with "…

printing/cups_config_helper.py

 #!/usr/bin/env python
 # Copyright (c) 2011 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.
 
 """cups-config wrapper.
 
 cups-config, at least on Ubuntu Lucid and Natty, dumps all
 cflags/ldflags/libs when passed the --libs argument.  gyp would like
 to keep these separate: cflags are only needed when compiling files
 that use cups directly, while libs are only needed on the final link
 line.
 
 This can be dramatically simplified or maybe removed (depending on GN
 requirements) when this is fixed:
   https://bugs.launchpad.net/ubuntu/+source/cupsys/+bug/163704
 is fixed.
 """
 
 import os
 import subprocess
 import sys
 
 def usage():
-  print 'usage: %s {--api-version|--cflags|--ldflags|--libs|--libs-for-gn}' % \
-      sys.argv[0]
+  print ('usage: %s {--api-version|--cflags|--ldflags|--libs|--libs-for-gn} '
+         '[sysroot]' % sys.argv[0])
 
 
 def run_cups_config(cups_config, mode):
   """Run cups-config with all --cflags etc modes, parse out the mode we want,
   and return those flags as a list."""
 
   cups = subprocess.Popen([cups_config, '--cflags', '--ldflags', '--libs'],
                           stdout=subprocess.PIPE)
   flags = cups.communicate()[0].strip()
 
@@ skipping 19 matching lines @@
 
   return flags_subset
 
 
 def main():
   if len(sys.argv) < 2:
     usage()
     return 1
 
   mode = sys.argv[1]
-  if len(sys.argv) > 2:
+  if len(sys.argv) > 2 and sys.argv[2]:
     sysroot = sys.argv[2]
     cups_config = os.path.join(sysroot, 'usr', 'bin', 'cups-config')
     if not os.path.exists(cups_config):
       print 'cups-config not found: %s' % cups_config
       return 1
   else:
     cups_config = 'cups-config'
 
   if mode == '--api-version':
     subprocess.call([cups_config, '--api-version'])
@@ skipping 20 matching lines @@
         print '"%s", ' % lib[2:]
     print ']'
   else:
     print ' '.join(flags)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())