GitLab

Changes:
1. Allowing the snapped window that next to the origin of the work area
   can be moved outside of the bounds of work area.
2. Delete RestackWindows in SplitViewController, since left and right
   snapped window will not overlap now.

Bug: 775236
Change-Id: Ib1d12443f8b9965544014590b8eff37ed8b3f665
Reviewed-on: https://chromium-review.googlesource.com/741489
Commit-Queue: min c <minch@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513052}