GitLab

Use OnceCallback instead of Callback, and CompletionOnceCallback instead
of CompletionCallback, in ChannelIDService.  Also restructure

ChannelIDService::JoinToInFlightRequest() to use early return if in
flight request in not found.

Bug: 807724
Change-Id: I45b55b0713ca9460fda8480d4f8ac14d5ead4435
Reviewed-on: https://chromium-review.googlesource.com/1117029Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570844}