GitLab

The autotestPrivate API provides the information of a window,
but I guess some properties might not be very clear to every
developers. I added comments to some of them, I hope some things
are a bit clearer without looking into the code.

Bug: none
Test: none
Change-Id: Iee076c45a89b0fdd8382f200cc584b86f3512671
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1907269Reviewed-by: Ricardo Quesada <ricardoq@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714292}