GitLab

The function "AddItem" add invisible empty menu for extension overflow menu.
It might be workaround to resolve appkit menus bug. But, it might be resolve.
The empty menu added before extension overflow menu is invisible, but
it has margins. So, the exetension overflow menu view in AppMenu looks
different in Windows and Mac.

Bug: NONE
Change-Id: Iba0b944f688b42a42d2e83716209770acae689e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1669136Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Sangseok Jang <sangseok.jang@navercorp.com>
Cr-Commit-Position: refs/heads/master@{#671884}