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This CL implements the new specs of the mini_views and the new desk
button borders, which are designed to have a gap between the view's
contents and the border so it's more obvious against white/light
contents or background.

Only the active, highlighted, or hovered-over mini_views will have borders.

Demo: https://bugs.chromium.org/p/chromium/issues/detail?id=996490#c9

BUG=1001230, 996490
TEST=Manually

Change-Id: Iedd05a55ec36b9c6193c80f36e1d0d252ef93412
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796112
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695407}