GitLab

This is a reland of c08274e9

The CL was previously reverted because the viewport activation test is
flaky, probably due to uncertain timing of near-the-viewport activation.
I've updated the test to only test for in-the-viewport activation,
I'll investigate further on why it's flaky for near-the-viewport
(manual testing shows activation happens consistently).

SHERIFFS: please don't revert this CL if it introduces a new flaky test.
Instead, please disable them and I'll investigate.

Original change's description:
> DL: Don't include skip-viewport-activation subtrees in the AX tree
>
> Now both render-subtree: skip-viewport-activation and skip-activation
> subtrees are not in the AX subtree at all, as discussed in
> https://github.com/WICG/display-locking/issues/102#issuecomment-564205445
>
> Now only render-subtree:invisible subtrees are in the AX tree, and they
> are automatically marked as offscreen because the nodes are activated
> when they are on screen.
>
> Bug: 1001930
> Change-Id: I1de511672f60078a02b3ddf3d989f2da1c44ae9d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2028883
> Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
> Reviewed-by: vmpstr <vmpstr@chromium.org>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#740531}

Bug: 1001930
Change-Id: Icdf43cff86ade7e7e8f2aee76933dfc51e3f022c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2054649Reviewed-by: vmpstr <vmpstr@chromium.org>
Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742520}