GitLab

Initial approach where the sidenav gets hidden/shown without
any animation. Also there is a visible flash in the plugin area
as a result of repainting after the sidenav is closed, which will
have to be addressed in follow up polish.

Bug: 1110015
Change-Id: I879198d6d90d2f384998be56186a3fd7f1aabd0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324202
Auto-Submit: dpapad <dpapad@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792812}