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- Support independent alt-tab mode selection for multi-profile.
- Save alt-tab mode to active user prefs and restore after a re-login
and a crash.

Bug: 1157105
Test: Manual test, `ash_unittests --gtest_filter=MultiUserWindowCycleControllerTest.*`
Change-Id: I59208f3f9726e776a10f0761c8aa431bf11b2080
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2616320Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Cattalyya Nuengsigkapian <cattalyya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843922}