Use std::ignore rather than ignore_result in base/

Bug: 1285085
Change-Id: I5cc94859f40db81190ca4d65f90e40891ae6224a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3371181


Reviewed-by: danakj chromium <danakj@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#962180}