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As we introduced paddings of the buttons inside oobe dialog - external overlay
is not displayed properly (see bug for screenshots).

Also use the overlay on the enrollment screen

Fixed: 1013337, b/143346960
Test: manual on the device
Change-Id: I22a1cf67c39221c378b0a5a6f0c7d5ab978287af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1892963Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712618}