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Replaces the old three view setup which was used before we could
apply rounded corners directly on layers. Tested manually on
LTR and RTL on all 4 orientations. Visually no difference.

Ran ui.OverviewDragWindowPerf.drag_to_snap. Not noticeable
improvements on caroline, but input latency goes from 95ms to 80ms
on krane.

Test: added tests
Bug: 1047778
Change-Id: Idff6345fb5778d2e898bc51cd76bd7eac3c1741d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033564
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738262}