Change weave::Device::Register API to async version Implementation of this function is the only place using HttpClient::SendRequestAndBlock. BUG:24267885 Change-Id: I8ebd34537ce42214ce262795b940923f3b11da79 Reviewed-on: https://weave-review.googlesource.com/1279 Reviewed-by: Alex Vakulenko <avakulenko@google.com>