Add --changes flag to buildbucket.py's put subcommand

buildbucket.py

 #!/usr/bin/env python
 # Copyright (c) 2015 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.
 
 """Tool for interacting with Buildbucket.
 
 Usage:
   $ depot-tools-auth login https://cr-buildbucket.appspot.com
   $ buildbucket.py \
@@ skipping 34 matching lines @@
   put_parser.add_argument(
     '-b',
     '--bucket',
     help=(
       'The bucket to schedule the build on. Typically the master name, e.g.'
       ' master.tryserver.chromium.linux.'
     ),
     required=True,
   )
   put_parser.add_argument(
+    '-c',
+    '--changes',
+    help='A flie to load a JSON list of changes dicts from.',
+  )
+  put_parser.add_argument(
     '-n',
     '--builder-name',
     help='The builder to schedule the build on.',
     required=True,
   )
   put_parser.add_argument(
     '-p',
     '--properties',
     help='A file to load a JSON dict of properties from.',
   )
   args = parser.parse_args()
   # TODO(smut): When more commands are implemented, refactor this.
   assert args.command == 'put'
 
+  changes = []
+  if args.changes:
+    try:
+      with open(args.changes) as fp:
+        changes.extend(json.load(fp))
+    except (TypeError, ValueError):
+      sys.stderr.write('%s contained invalid JSON list.\n' % args.changes)
+      raise
+
   properties = {}
   if args.properties:
     try:
       with open(args.properties) as fp:
         properties.update(json.load(fp))
     except (TypeError, ValueError):
       sys.stderr.write('%s contained invalid JSON dict.\n' % args.properties)
       raise
 
   authenticator = auth.get_authenticator_for_host(
     BUILDBUCKET_URL,
     auth.make_auth_config(use_oauth2=True),
   )
   http = authenticator.authorize(httplib2.Http())
   http.force_exception_to_status_code = True
   response, content = http.request(
     PUT_BUILD_URL,
     'PUT',
     body=json.dumps({
       'bucket': args.bucket,
       'parameters_json': json.dumps({
         'builder_name': args.builder_name,
+        'changes': changes,
         'properties': properties,
       }),
     }),
     headers={'Content-Type': 'application/json'},
   )
 
   if args.verbose:
     print content
 
   return response.status != 200
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))