I suspect it's either https://chromium-review.googlesource.com/c/chromium/src/+/772290 or https://chromium-review.googlesource.com/692704. Will try reverting one, then the other. :)

Reverting https://chromium-review.googlesource.com/692704 in https://chromium-review.googlesource.com/c/chromium/src/+/778859.

Revert failed due to changes between Friday and now. Poking at it to see how bad the diff is.

Tried and failed to get this fixed. Deferring to dmazzoni@, who should be waking up soon? :) :)

I'll either fix or disable the tests right now.

This was actually the change that caused the failure:

https://chromium-review.googlesource.com/c/chromium/src/+/772290

Fix here:

https://chromium-review.googlesource.com/#/c/chromium/src/+/779062

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3045acb501991e37fb2416ab8816d2ff4e66735f

commit 3045acb501991e37fb2416ab8816d2ff4e66735f
Author: Dominic Mazzoni <dmazzoni@chromium.org>
Date: Mon Nov 20 22:33:17 2017

No AX live region event on removing a node.

This code was leading to a UAF on Mac. Disable one
test for now, will need to revisit once we find a safer
way to fire that event.

Bug:  786848 
Change-Id: Ib862874ea149ee3751cbbff4d955f03987918737
Reviewed-on: https://chromium-review.googlesource.com/779062
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517956}
[modify] https://crrev.com/3045acb501991e37fb2416ab8816d2ff4e66735f/content/browser/accessibility/dump_accessibility_events_browsertest.cc
[modify] https://crrev.com/3045acb501991e37fb2416ab8816d2ff4e66735f/ui/accessibility/ax_event_generator.cc

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