The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c0c709de4223ff4875be04d8ebe3baac6b2c6b9b

commit c0c709de4223ff4875be04d8ebe3baac6b2c6b9b
Author: Ivan Sandrk <isandrk@google.com>
Date: Wed Feb 21 14:47:12 2018

Close devtools on entering/exiting locked fullscreen mode

Any running devtools instances are a security liability in the locked fullscreen
mode as they may allow the user to escape the mode. Shut down all devtool
instances on entering/exiting this special mode.

Also do a small refactoring of the code for this feature inside tabs_api.cc.

Bug:  chromium:812662 
Change-Id: Ib66b59093ff1f8ec2e76dcd2f776100bd96f9344
Reviewed-on: https://chromium-review.googlesource.com/922203
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Ivan Šandrk <isandrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538098}
[modify] https://crrev.com/c0c709de4223ff4875be04d8ebe3baac6b2c6b9b/chrome/browser/extensions/api/tabs/tabs_api.cc
[modify] https://crrev.com/c0c709de4223ff4875be04d8ebe3baac6b2c6b9b/chrome/browser/ui/browser_command_controller.cc

As verified on M66.0.3359.28 10452.8.0 dev parrot, devtools is not available during locked full screen mode and is available after exiting the full screen mode.