GitLab

Adds a toolbar to the implementation to showcase, which helps
demostrating how the alert respects the safe areas. The toolbar contains
a dummy button to demostrate how the presentation is done not modally.

R=edchin

Bug: 951301, 951300
Change-Id: I31297cfc73a0e59b854404685cdb1d4851f12bfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594584
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658498}