splitview: Make split view work as expected with multiprofile.

BEFORE: On switching away from a user session in split view, the split
view divider is seen in the newly activated user session where any
windows are maximized. It looks horribly wrong.
AFTER: The split view state on switching away from a user session is
restored on switching back to it.

Test: manual
Bug: 833685
Change-Id: If5f1721d9015f59615e212425c2b8f21838572e7
Reviewed-on: https://chromium-review.googlesource.com/c/1389695
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624363}
3 files changed