The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f2e52582169d42ef9a3f836b8125c755ce7b1eee

commit f2e52582169d42ef9a3f836b8125c755ce7b1eee
Author: Aaron Leventhal <aleventhal@chromium.org>
Date: Thu May 31 19:25:56 2018

Fire active descendant event when matching descendant added later

When aria-activedescendant points to a nonexistent element, or an element that does not yet have
accessible object, and that element is later added to the AX tree, an event needs to be fired,
when the element with the aria-activedescendant is focus. Without this, a screen reader will not be aware of the focus in some cases.

The fix is to check aria-activedescendant values when an object created. If the object being
created is already pointed to by a valid aria-activedescendant on the currently focused object,
treat it internally like an aria-activedescendant attribute change.

Bug:  847245 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ia8442e85ceb7f6c8719fb6f4d72a35d70b97b732
Reviewed-on: https://chromium-review.googlesource.com/1071689
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563344}
[modify] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/browser/accessibility/dump_accessibility_events_browsertest.cc
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-add-list-expected-mac.txt
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-add-list-expected-win.txt
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-add-list.html
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-show-list-expected-mac.txt.html
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-show-list-expected-win.txt.html
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/content/test/data/accessibility/event/aria-combo-box-delay-show-list.html
[add] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/third_party/WebKit/LayoutTests/accessibility/aria-combo-box-with-delay-add.html
[modify] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.cc
[modify] https://crrev.com/f2e52582169d42ef9a3f836b8125c755ce7b1eee/third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h