GitLab

If no buttons are shown in the shelf navigation widget, we should hide
the widget background, too.

BUG=1012814

Change-Id: I6763c6719d256b2b07b74c06948af96074ae4851
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2025636Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736007}