Add "Don't show this again" button to privet printer notifications

This button globally disables privet notifications using the
enable_notifications preference. Once users click it, they should not see
notifications again.

BUG=297337
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/24316006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225079 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225079