The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/95114dfaac1b5fcdc83beded34599b5869c7c463

commit 95114dfaac1b5fcdc83beded34599b5869c7c463
Author: Mitsuru Oshima <oshima@chromium.org>
Date: Fri Sep 08 00:41:35 2017

Don't move lock screen wallpaper window in unified desktop mode.

It's not clear why I did this, but wallpaper window gets
created on the new root window.

Bug= 761413 
Test=Updated the unit test. Tested on device too.

Change-Id: Id165cc72897ae644e087d980c227b109a804e96d
Reviewed-on: https://chromium-review.googlesource.com/653362
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500454}
[modify] https://crrev.com/95114dfaac1b5fcdc83beded34599b5869c7c463/ash/root_window_controller.cc
[modify] https://crrev.com/95114dfaac1b5fcdc83beded34599b5869c7c463/ash/root_window_controller_unittest.cc