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This CL creates OverlayPresenterUIDelegateImpl, which handles the UI
for OverlayPresenters.  Additionally, it adds
OverlayContainerCoordinator, which provides the presentation context
upon which to present requested overlay UI.

Bug: 941745
Change-Id: Id44c906952260fbd0cb9e7f541c93fd70d2d7d4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614696
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664003}