Activate invisible elements when focusing happens

When an invisible element needs to be focused, for example with the
focus() method or through tabindex navigation, we will send the
activateinvisible event and focus the element. If the event's default
action is prevented and the element stays invisible, we will focus on
the next in order when appropriate.

Bug: 873057
Change-Id: Ieb47823e5bdfadc3477127c56d7a2db1598cb524
Reviewed-on: https://chromium-review.googlesource.com/c/1381363
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625934}
7 files changed