GitLab

Adds an inset when the shelf is auto hidden because we want the grid to
be centered as if the shelf is fully visible.

Test: ash_unittests WindowSelectorTest.GridBounds
Bug: 908679, 908982
Change-Id: Ibccfb0bab70d68a463c3325fa8ca3b7912d0dc65
Reviewed-on: https://chromium-review.googlesource.com/c/1354355Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612859}