FYI the FocusOutlineManager class can be used to deal with this problem, see [1] and an example at [2]


[1] https://cs.chromium.org/chromium/src/ui/webui/resources/js/cr/ui/focus_outline_manager.js
[2] https://cs.chromium.org/chromium/src/ui/webui/resources/cr_elements/cr_toggle/cr_toggle.js?l=94

FYI, candidate fix is at https://chromium-review.googlesource.com/c/chromium/src/+/749887.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ce67f79b1082968e5a0597572837cd6de6edcb9e

commit ce67f79b1082968e5a0597572837cd6de6edcb9e
Author: dpapad <dpapad@chromium.org>
Date: Fri Nov 10 02:17:08 2017

MD Extensions: Fix FocusOutlineManager to work for Shadow DOM.

FocusOutlineManager previously deferred updating the focus-outline-visible
CSS class until a 'focus' event was received. This does not work in Shadow DOM,
since 'focus' events do not reach the top level document element. Updating
focus-outline-visible CSS class when a mouse or keyboard event occurs fixes the issue.

Note: This slightly changes the behavior of FocusOutlineManager when
1) an element is focused by keyboard
2) while the element is focused the user clicks on it.

Before, the focus outline would remain visible (introduced at crrev.com/22521002/).
After, clicking on an element that already shows the outline will remove the outline.

Bug:  772571 , 781459 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ie233c212fd17724ca8a43e46eb51398612644331
Reviewed-on: https://chromium-review.googlesource.com/749887
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515424}
[modify] https://crrev.com/ce67f79b1082968e5a0597572837cd6de6edcb9e/chrome/browser/resources/md_extensions/compiled_resources2.gyp
[modify] https://crrev.com/ce67f79b1082968e5a0597572837cd6de6edcb9e/chrome/browser/resources/md_extensions/error_page.html
[modify] https://crrev.com/ce67f79b1082968e5a0597572837cd6de6edcb9e/chrome/browser/resources/md_extensions/error_page.js
[modify] https://crrev.com/ce67f79b1082968e5a0597572837cd6de6edcb9e/ui/webui/resources/js/cr/ui/focus_outline_manager.js