Migrate WebApkInstallService::FinishCallback to use OnceCallback.

Also fixed lint errors in modified files.

Bug: 714018
Change-Id: I1a5347e8adab28edabebb386e5e5ef20b6ebe938
Reviewed-on: https://chromium-review.googlesource.com/1117374
Reviewed-by: Xi Han <hanxi@chromium.org>
Commit-Queue: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571613}
6 files changed