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This CL adds files and plumbing for the UI bubble for profile
customization.

The bubble is behind an experimental flag. The actual content of the
bubble will be implemented in javascript in a follow up CL, in this CL
there is only a title and a button that does nothing:
https://screenshot.googleplex.com/3JhvoT3kTgXMQ4Y.png

Bug: 1130945
Change-Id: I1fab6184a69b3e86a474e9bb896e64f2f79dcbab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2431567Reviewed-by: Monica Basta <msalama@chromium.org>
Commit-Queue: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813126}