Convert Callback usage to {Once,Repeating}Callback in V8 values and post-task

The PostTaskToInProcessRendererAndWait() method can take a OnceCallback
since it runs it once, so we do, and callers are changed use BindOnce().

The V8ValueConverter takes a Callback which it never uses, so remove it
from the parameters instead of converting it to an appropriate type.

A few other simple conversions in content/renderer/worker and service_worker.

R=avi@chromium.org

Bug: 953861
Change-Id: I8e77532b6d5e40b5961b6f5193acde6bc9818389
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623489
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662297}
21 files changed