Invalidate continue section layout when children state changes

Hiding or showing suggestions container or privacy toast changes the
continue section preferred size - call PreferredSizeChanged in those
situations to request app list view layout update, so the continue
section gets sized according to new preferred size.

BUG=1314205

Change-Id: If582675067b8777485ea956ecb63183905314eca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3575688
Reviewed-by: Ana Salazar <anasalazar@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#990031}