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This requires some changes to WindowMiniView to make it more
customizeable as UX specifically only wants shadows on overview and not
alt-tab. Changes made were to apply effects on an icon supplied through
a window property, in this case a shadow.

Also, adding shadow to a label will shift the text. Since we want to
keep the text right aligned with the icon, make OverviewItemView
header layout code custom (previously was using the default from
WindowMiniView FlexLayout).

Test: manual
Fixed: 1028845
Change-Id: Ief8e9bbccc42fa198ff31729b735edc519d78270
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128835Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755964}