Navi: Add grid of NTP backgrounds

https://i.imgur.com/jTePPEf.png
https://i.imgur.com/1iWYFnE.png
Keyboard focused: https://i.imgur.com/pES0fsP.png

Bug: 924176
Change-Id: I60c90e0004c11cd6d31eb062ae367c0c89aa14bf
Reviewed-on: https://chromium-review.googlesource.com/c/1459793
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631351}
6 files changed