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When in overview mode, if a window is closed, then the rest of the windows
that behind the closed window in the stack are moved on step forward. However,
if there are no windows behind the closed window, then move the windows in
front of the closed window backward one step.

BUG=408280
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/531093003

Cr-Commit-Position: refs/heads/master@{#293196}