Add new subcommand for 'Changes Submitted Together'.

We may need to submit a chain of CLs. With this sub-cmd, we could
track their revisions along the chain, without querying them one
by one.

BUG=1236658
TEST=local run

Change-Id: If5930fb8f01daccff4d7c5c5e91c8db8887d8e47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3098095Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Xinan Lin <linxinan@chromium.org>

gerrit_client.py

@@ -248,6 +248,17 @@ def CMDsubmitchange(parser, args):
   write_result(result, opt)
 
 
+@subcommand.usage('[args ...]')
+def CMDchangesubmittedtogether(parser, args):
+  """Get all changes submitted with the given one."""
+  parser.add_option('-c', '--change', type=int, help='change number')
+  (opt, args) = parser.parse_args(args)
+  result = gerrit_util.GetChangesSubmittedTogether(
+      urlparse.urlparse(opt.host).netloc, opt.change)
+  logging.info(result)
+  write_result(result, opt)
+
+
 @subcommand.usage('[args ...]')
 def CMDgetcommitincludedin(parser, args):
   """Retrieves the branches and tags for a given commit."""

gerrit_util.py

@@ -743,6 +743,13 @@ def SubmitChange(host, change):
   return ReadHttpJsonResponse(conn)
 
 
+def GetChangesSubmittedTogether(host, change):
+  """Get all changes submitted with the given one."""
+  path = 'changes/%s/submitted_together?o=NON_VISIBLE_CHANGES' % change
+  conn = CreateHttpConn(host, path, reqtype='GET')
+  return ReadHttpJsonResponse(conn)
+
+
 def PublishChangeEdit(host, change, notify=True):
   """Publish a Gerrit change edit."""
   path = 'changes/%s/edit:publish' % change