GitLab

Use CompletionOnceCallback instead of CompletionCallback, and
CancelableCompletionOnceCallback instead of CancelableCompletionCallback
in //content/browser/appcache.

Bug: 807724

This exact CL has been reviewed and approved at
https://crrev.com/c/1163933.  However, due to a bug in Gerrit, I
inadvertently submitted that CL skipping the CQ.  See
https://crbug.com/872722.  That CL was reverted, and now I am relanding
it properly in this CL, through CQ this time.  Original reviewer is
TBR'd.

TBR=kinuko@chromium.org

Change-Id: Ie1d8e275e754cc51457aca6537ad08b228cfaaac
Reviewed-on: https://chromium-review.googlesource.com/1169307Reviewed-by: Bence Béky <bnc@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581894}