[Chrome Colors] Add third-party theme information to Colors menu.

This CL only displays the theme information. The functionality for
'Uninstall' button will be in the followup.

Light mode: https://screenshot.googleplex.com/Tn3Zn5boRtR.png
Dark mode: https://screenshot.googleplex.com/V264CrOOQMW.png
RTL: https://screenshot.googleplex.com/uVvmSrSitDM.png

Bug: 976420
Change-Id: Id6c98bd56f454481163ed1ce6b12457c57cd0441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1679169
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Reviewed-by: Kristi Park <kristipark@chromium.org>
Reviewed-by: Martin Barbella <mbarbella@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673586}