Initial support for Clipboard Permission

This is just the Webkit side of the permission. A follow-up cl will
add UX support and hook up clipboard code to use this permission.

Bug: 677564
Change-Id: If944340769c0192a9e123b7fc4b57b22b0619cac
Reviewed-on: https://chromium-review.googlesource.com/720158
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Jeffrey Yasskin <jyasskin@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: Gary Kacmarcik <garykac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512248}
8 files changed