GitLab

A followup patch should use AXID throughout the code base, but that would be a much larger change.
Also makes a few cosmetic changes to AXTree to ease understanding.
R=aboxhall@chromium.org

Change-Id: I78c9843f4b234312b7529ecf832ef41a666caad5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696272
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Auto-Submit: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681363}