[NTP] Don't preview a preselected bg tile

Bug: 937570
Change-Id: I2d4f0134a3734195082ecc5c003b5542a91cad30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1728427
Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682960}
1 file changed