Add video to AmbientModeAnimationTheme metrics enum.

Bug: b:271182121
Change-Id: I54dd2e7d16374828dcb720a4749e573207718daa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4568366


Reviewed-by: Jason Thai <jasontt@chromium.org>
Commit-Queue: Eric Sum <esum@google.com>
Cr-Commit-Position: refs/heads/main@{#1149424}