[tab_under] Hook into the new desktop UI

This doesn't properly plumb through the click closure, which might need
some rethinking since we share the UI with framebusting.

Bug: 661629
Change-Id: I8a38140eee2f314e98183fc0874af94dda15a626
Reviewed-on: https://chromium-review.googlesource.com/763909
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Patrick Monette <pmonette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521442}
2 files changed