update_engine: Run clang-format on payload_consumer

We just did a AOSP merge, so it is a good time to clean things up.

BUG=none
TEST=unittest

Change-Id: I4fe9cef5eb8709344d6b78bc298c0f1c03308ffc
Reviewed-on: https://chromium-review.googlesource.com/1407540


Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>
Reviewed-by: Xiaochu Liu <xiaochu@chromium.org>