Add a "guard" content settings type for chooser permissions.

Add a "guard" content settings type for chooser permissions.

This content setting should default to allow, but can be set to deny by
group policy in order to disable a feature that normally grants
permissions by prompting the user with a chooser.

The new CanRequestObjectPermission() function should be called by the
chooser UI before showing the user anything and cause the request to
fail if permission is denied.

BUG=529950

[Reilly Grant (use Gerrit), 2015-11-11 00:36:27]

reillyg@chromium.org changed reviewers:
+ mlamouri@chromium.org, raymes@chromium.org

[Reilly Grant (use Gerrit), 2015-11-11 00:36:27]

mlamouri@chromium.org: Please review changes in chrome/browser/permissions.

raymes@chromium.org: Please review changes in components/content_settings.

[raymes, 2015-11-11 02:38:26]

The code lg but I'm wondering now if we should hold off on adding this until we
have a user of it lined up. Is there a plan to add a global toggle to site
settings? Or an enterprise pref?

[mlamouri (slow - plz ping), 2015-11-23 17:53:22]

IIRC, you suggested adding this Raymes. I told Reilly to move this to split this
to a different CL to make things easier. If you think this feature is no longer
needed, maybe we should put this aside?

[raymes, 2015-11-23 23:50:01]

On 2015/11/23 17:53:22, Mounir Lamouri wrote:
> IIRC, you suggested adding this Raymes. I told Reilly to move this to split
this
> to a different CL to make things easier. If you think this feature is no
longer
> needed, maybe we should put this aside?

Agreed - Reilly and I chatted and decided to hold off on this for the time
being.