[EoS] Enable the Explore Sites tile in the Most Visited section.

This integrates the new tiletype inside of most likely similarly to the
homepage tile - it inserts itself at the end of the new suggestions.

Bug: 966024
Change-Id: Ifd24a60415aa2eb35ed49bd2ffa760814dfdc191
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1629032
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664549}