Ensure notifications are shown even if animation is cancelled

The ChromeVox notification would often fail to animate onto the
screen when ChromeVox was enabled due to the screen layout change
when the ChromeVox bar was added. This ensures notifications are
drawn on screen even when animation is cancelled midway.

Bug: b:444156438
Test: Manual, new unittest
Change-Id: Icaf6027236bb9a108109149b30ef3c201b832f3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7241108
Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1558284}