Initial desktop UX support for Clipboard Permission

This adds the content setting for the new Async Clipboard API
and the UX plumbing. This is behind the kClipboardContentSetting
feature flag.

Bug: 677564
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I59ec221057fc6dd73ca830b1d6889ac40b44be68
Reviewed-on: https://chromium-review.googlesource.com/750200
Commit-Queue: Gary Kacmarcik <garykac@chromium.org>
Reviewed-by: Patti <patricialor@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518524}
25 files changed