gn bootstrap.py: Fixed attrib error "no_bootstrap"

tools/gn/bootstrap/bootstrap.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """Bootstraps gn.
 
 It is done by first building it manually in a temporary directory, then building
 it with its own BUILD.gn to the final destination.
 """
@@ skipping 60 matching lines @@
     build_rel = os.path.join('out', 'Release')
   build_root = os.path.join(SRC_ROOT, build_rel)
 
   try:
     with scoped_tempdir() as tempdir:
       print 'Building gn manually in a temporary directory for bootstrapping...'
       build_gn_with_ninja_manually(tempdir, options)
       temp_gn = os.path.join(tempdir, 'gn')
       out_gn = os.path.join(build_root, 'gn')
 
-      if options.no_bootstrap:
+      if options.no_rebuild:
         mkdir_p(build_root)
         shutil.copy2(temp_gn, out_gn)
       else:
         print 'Building gn using itself to %s...' % build_rel
         build_gn_with_gn(temp_gn, build_rel, options)
 
       if options.output:
         # Preserve the executable permission bit.
         shutil.copy2(out_gn, options.output)
   except subprocess.CalledProcessError as e:
@@ skipping 306 matching lines @@
     cmd.append('-v')
   cmd.append('gn')
   check_call(cmd)
 
   if not debug:
     check_call(['strip', os.path.join(build_dir, 'gn')])
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))