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Going into overview mode makes all the windows visible. At the end of the
overview mode, make sure the windows that aren't visible (i.e. windows
other than the active window, or the left/right windows in split-view mode)
are marked as hidden correctly.

BUG=none
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/525443002

Cr-Commit-Position: refs/heads/master@{#292682}