Entry point for focus mode

When clicking "focus this tab", the current tab should be brought to a new
Focus Mode Window.

Bug: 939537
Change-Id: I7f790f0f906b775a8a9bdc21b991747bd289f643
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1509797
Commit-Queue: Yining Wang <yiningwang@google.com>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642640}
9 files changed