Refactor out TileView to be common widget

This is to facilitate sharing between explore sites and most likely tiles.

Bug: 867488
Change-Id: Ic84c2a5363318bea6e7237085d4df9f346b09891
Reviewed-on: https://chromium-review.googlesource.com/1213706
Commit-Queue: Cathy Li <chili@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591537}
15 files changed