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Adds a flag to the upgrade sign-in flow to use the new sign-in
architecture and updates the user sign-in coordinator to ensure
that the orientation restrictions are applied.

Bug: 971989
Change-Id: I9f844029ba81b54c396d72d62e50ea565bf28b24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120501Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753611}