[iOS] Animated promo bug: Lottie background color not applied

Fixing the bug that the lottie animation's background color is not
applied until a trait collection change. Also adds the background color
to the safari export education screen.

Bug: N/A
Change-Id: Idb98e473414a5b37497ad054ef4182281eb7dcbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6817963
Reviewed-by: Benjamin Williams <bwwilliams@google.com>
Commit-Queue: Ginny Huang <ginnyhuang@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Ginny Huang <ginnyhuang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1496483}