GitLab

* Init members in declaration
* Use =default
* Shorten code
* Use enum names instead of constant values
* Add comments
* Better use of auto
* Remove some bare news
* Remove using declarations

Bug: none
Change-Id: I710527a697406510143575ec4d582c5b5b37a071
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1983508
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728803}