ChromeVox should update focus ring when focused object animates.

Bug: 761164
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ib1873608cd586bbcb43cb79d7d1754ade52f2fa7
Reviewed-on: https://chromium-review.googlesource.com/780402


Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518272}