The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/891ceec45f09bcc6664ad1fcb0684e16f7a3d053

commit 891ceec45f09bcc6664ad1fcb0684e16f7a3d053
Author: yuzus <yuzus@chromium.org>
Date: Thu Apr 07 09:46:45 2016

Skip shadow hosts with negative tabindex in focus navigation

This CL implements a new focus navigation behavior with negative index-ed shadow hosts; Shadow hosts with negative tabindex and their descendants are completely skipped.
See the spec here: https://w3c.github.io/webcomponents/spec/shadow/#sequential-focus-navigation

BUG= 600621 

Review URL: https://codereview.chromium.org/1862563002

Cr-Commit-Position: refs/heads/master@{#385701}

[modify] https://crrev.com/891ceec45f09bcc6664ad1fcb0684e16f7a3d053/third_party/WebKit/LayoutTests/fast/dom/shadow/resources/shadow-dom.js
[modify] https://crrev.com/891ceec45f09bcc6664ad1fcb0684e16f7a3d053/third_party/WebKit/LayoutTests/shadow-dom/focus-navigation-with-delegatesFocus-expected.txt
[modify] https://crrev.com/891ceec45f09bcc6664ad1fcb0684e16f7a3d053/third_party/WebKit/LayoutTests/shadow-dom/focus-navigation-with-delegatesFocus.html
[add] https://crrev.com/891ceec45f09bcc6664ad1fcb0684e16f7a3d053/third_party/WebKit/LayoutTests/shadow-dom/focus-with-negative-index.html
[modify] https://crrev.com/891ceec45f09bcc6664ad1fcb0684e16f7a3d053/third_party/WebKit/Source/core/page/FocusController.cpp