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Define SPLITVIEW_ANIMATION_RESTORE_OVERVIEW_WINDOW. And also animate the
overview window from its position in overview grid to its snapped postion.

Bug: 822486
Change-Id: I64a48b33012c428a5529dfea58f048f30c043e73
Reviewed-on: https://chromium-review.googlesource.com/972562Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545580}