Add the chromium ninja builder to the list of trybots for a DEPS roll.

tools/roll_deps.py

 #!/usr/bin/python2
 
 # Copyright 2014 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Skia's Chromium DEPS roll script.
 
 This script:
@@ skipping 27 matching lines @@
 
 DEFAULT_BOTS_LIST = [
     'android_clang_dbg',
     'android_dbg',
     'android_rel',
     'cros_daisy',
     'linux',
     'linux_asan',
     'linux_chromeos',
     'linux_chromeos_asan',
+    'linux_chromium_gn_dbg',
     'linux_gpu',
     'linux_layout',
     'linux_layout_rel',
     'mac',
     'mac_asan',
     'mac_gpu',
     'mac_layout',
     'mac_layout_rel',
     'win',
     'win_gpu',
@@ skipping 475 matching lines @@
     if not git_utils.git_executable():
         option_parser.error('Invalid git executable.')
 
     config = DepsRollConfig(options)
     find_hash_and_roll_deps(config, options.revision, options.git_hash)
 
 
 if __name__ == '__main__':
     main(sys.argv[1:])