The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/28f7bafe25da6d6b0f4f01b3328eb347b04fa172

commit 28f7bafe25da6d6b0f4f01b3328eb347b04fa172
Author: sawtelle <sawtelle@google.com>
Date: Tue Jun 12 17:35:56 2018

[Picture in Picture] Launch PiP window on active screen.

This change will make it so that when a PiP window is launched,
it will get the active screen and attach it to the
bottom right there. Previously it would do this on the primary
screen.

Manually tested in the following ways:
1) Open browser on primary screen, launch PiP window. Close PiP
window, move browser to another screen, relaunch PiP window.
Confirm that PiP window launches on second screen.

2) Open browser on primary screen, move to other screen. Launch
PiP window. Confirm that PiP window launches on second screen.

3) Open browser on non-primary screen, launch PiP window. Close PiP
window, move browser to primary screen, relaunch PiP window.
Confirm that PiP window launches on primary screen.

4) Open browser on primary screen, launch PiP window. Move
browser to another screen, and without closing original PiP
window relaunch PiP window. Confirm that the PiP window is
removed from the primary screen and launches on the second
screen.

Bug:  830237 
Change-Id: If3b8e3c21015e04633702b8ee905dba6c7fbd852
Reviewed-on: https://chromium-review.googlesource.com/1089827
Reviewed-by: apacible <apacible@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Steven Sawtelle <sawtelle@google.com>
Cr-Commit-Position: refs/heads/master@{#566487}
[modify] https://crrev.com/28f7bafe25da6d6b0f4f01b3328eb347b04fa172/chrome/browser/ui/views/overlay/overlay_window_views.cc

As far as I know, this is fixed. Please reopen if I'm mistaken.