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Most of the times the screen has its implementation as the OOBE screen
(html + javascript). But it could happen that there is no html part. In
that case OobeScreenExitWaiter is useless because screen on the OOBE
part might not change.
This CL create a WizardController screen exit waiter. Which should help
in such cases.

Bug: none
Change-Id: I9e48e892a4e46d2f417d92a27d59b8319b8ce965
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2431046Reviewed-by: Yilkal Abe <yilkal@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811685}