dark_mode: Restart after toggle color mode.

Restart the chrome to let the color mode changes take effect. This is
added to provide a method for UX to do color audit, which will be
helpful for us to correct the incorrect colors in each color mode.

Will do colors live update in the next step.

Bug: 1106012
Change-Id: I451efd94e648680a55bf6f1f77cc9d92209d67ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392935


Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805539}