GitLab

* New PhoneHub tab to chrome://multidevice-internals
* Adds a toggle that when flipped on, will cause a FakePhoneHubManager
  to be used instead.

Screenshot: https://screenshot.googleplex.com/7dimKet6oWrzeR4

Bug: 1106937
Change-Id: Ib2697abfaf15153b394689a804ff5ff73994ed15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380608Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802851}