GitLab

The success and failure callbacks are only run once, so they can be
OnceCallbacks.

Introduces SuccessOnceCallback and FailureOnceCallback in
VpnService to avoid blowing the change up to the whole
VpnService API.

TBR=dcheng

Bug: 1007763
Change-Id: I668083ab94ecbb9a3c06e3ba8f60d72d493570f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1960891
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723585}