Use more idiomatic c++ and add slightly better comments.

Change-Id: Id6397a25851915eb10a0370d23dc41ca7fce3c2e
Reviewed-on: https://chromium-review.googlesource.com/c/1418194Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58937}