[iOS] Update FullscreenUIElement comments.

Bug: none
Change-Id: If6a770a3cc25a1c46bb04858851f55406740d214
Reviewed-on: https://chromium-review.googlesource.com/c/1479935
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Auto-Submit: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633968}
1 file changed