Following comment in crrev.com/c/3039331, submit call
is fully synchronous.

BUG=1207955
TEST=e2e

Change-Id: I9146d43b4d4530ad5064709e418d34e3229e19ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3049672
Commit-Queue: Xinan Lin <linxinan@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>