code health: Replace base::RunLoop for base::test::TestFuture

This change replaces the use of base::RunLoop to test async code with
the special wrapper base::test::TestFuture to improve clarity

Bug: b:266783937
Change-Id: I89413f773b97fa305e02d5af3fbeea45243fd299
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5413502


Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Commit-Queue: Ahmed Nasr <anasr@google.com>
Cr-Commit-Position: refs/heads/main@{#1281816}