GitLab

This CL adds heuristic logics in ARC accessibility to stabilize the
focus.

* On accessibility focus changed event from Android, update the focus
  stored in AXTreeSourceArc to the event source. TalkBack updates the
  accessibility focus on this event. Also by doing this, we can follow
  the accessibility foucsed node in a case like b:130186502.

* AXTreeSourceArc stores the previously focused node for each root
  window. By doing this, when a user open a ChromeVox menu or another
  window and comes back to the app, the focus remains on the same node.

AX-Relnotes: Improved accessibility focus handling in ARC apps.
Bug: 130186502
Bug: 151398335
Test: manual. described above. Also unit_tests.
Change-Id: Ib002f559569409bc5ef4ab8982174d61a096a3b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2398438
Commit-Queue: Hiroki Sato <hirokisato@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Reviewed-by: Sara Kato <sarakato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806846}