[Android] Don't use a device blacklist if one isn't provided.

build/android/screenshot.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 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.
 
 """Takes a screenshot or a screen video capture from an Android device."""
 
 import logging
 import optparse
@@ skipping 57 matching lines @@
 
   (options, args) = parser.parse_args()
 
   if len(args) > 1:
     parser.error('Too many positional arguments.')
   host_file = args[0] if args else options.file
 
   if options.verbose:
     logging.getLogger().setLevel(logging.DEBUG)
 
-  if options.blacklist_file:
-    blacklist = device_blacklist.Blacklist(options.blacklist_file)
-  else:
-    blacklist = None
+  blacklist = (device_blacklist.Blacklist(options.blacklist_file)
+               if options.blacklist_file
+               else None)
 
   devices = device_utils.DeviceUtils.HealthyDevices(blacklist)
   if options.device:
     device = next((d for d in devices if d == options.device), None)
     if not device:
       raise device_errors.DeviceUnreachableError(options.device)
   else:
     if len(devices) > 1:
       parser.error('Multiple devices are attached. '
                    'Please specify device serial number with --device.')
     elif len(devices) == 1:
       device = devices[0]
     else:
       raise device_errors.NoDevicesError()
 
   if options.video:
     _CaptureVideo(device, host_file, options)
   else:
     _CaptureScreenshot(device, host_file)
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())