GitLab

Adding a skeleton sidebar element with bookmarks/thumbnails icon buttons
and placeholder divs for the two views.

Bug: 1110756
Change-Id: I34b452bcc21a331c2eec88c15e794922b3124344
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324558Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793566}