The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/99029a1c9485daea9d1c642b6a733c81f22867a4

commit 99029a1c9485daea9d1c642b6a733c81f22867a4
Author: oshima <oshima@chromium.org>
Date: Wed Mar 30 23:14:30 2016

Allow unified desktop for 3+ displays

BUG= 599232 

Review URL: https://codereview.chromium.org/1845723002

Cr-Commit-Position: refs/heads/master@{#384140}

[modify] https://crrev.com/99029a1c9485daea9d1c642b6a733c81f22867a4/ash/display/display_manager.cc
[modify] https://crrev.com/99029a1c9485daea9d1c642b6a733c81f22867a4/ash/display/display_manager_unittest.cc