The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4d3efe522f320dd2abf86b70407be67d1901b98d

commit 4d3efe522f320dd2abf86b70407be67d1901b98d
Author: Jennifer Apacible <apacible@chromium.org>
Date: Fri Jul 06 22:17:59 2018

[Cocoa] Include borderless windows in the MacOS window cycle.

Currently, only framed windows are included for the MacOS window cycle,
which can be done with cmd+`. This change includes frameless windows,
such as the Picture-in-Picture window, to be part of this behavior.

Bug:  849957 
Change-Id: Iff96d45774d3b87fcee7a8f3fa0b1fefaa2469f3
Reviewed-on: https://chromium-review.googlesource.com/1124874
Commit-Queue: apacible <apacible@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573089}
[modify] https://crrev.com/4d3efe522f320dd2abf86b70407be67d1901b98d/ui/views/cocoa/bridged_native_widget.mm

Unable to reproduce the issue on Mac 10.13.5 using chrome 69.0.3455.0 build without fix.
After enabling #SufaceLayer objects for vdeos, #cocoa and # Picture-in-Picture at chrome://flags and navigated to "https://googlechrome.github.io/samples/picture-in-picture/", 
Hitted " cmd+` " as we have not observed that the window tabbing.

Attaching screen cast of build without fix for reference.

apacible@chromium.org@ - Could you please check the attached screen cast and please let us know if anything missed from our end. Also please provide steps to verify the issue from our end.

Thanks...!

Deleted: 849957.mp4 3.1 MB

	849957.mp4 3.1 MB View Download

Window tabbing refers to having multiple windows open, and being able to cycle between them.

To reproduce, enter PiP mode and then press cmd+` to cycle between the windows, rather than opening a new tab.

Unable to reproduce the issue on Mac 10.13.5 using chrome 69.0.3446.0 build without fix.

After enabling # Picture-in-Picture at chrome://flags, Hitted " cmd+` " as we have observed that the window tabbing.

Verified the fix on Mac 10.13.5 using Chrome version # 69.0.3487.0 as per the comment #4.

Attaching screen cast of build without and with fix for reference.

apacible@chromium.org@ - Could you please check the attached screen cast and please let us know if anything missed from our end. Also help in fixing this issue.

Thanks...!

Deleted: 849957.mp4 3.1 MB

	849957.mp4 3.1 MB View Download

Deleted: 849957-1.mp4 1.3 MB

	849957-1.mp4 1.3 MB View Download