Update privet notifications to not be printer specific

Instead of a specific notification per printer, show the generic messages "new
printer on your network" and "new printers on your network".  Show only one
notification globally.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/24335002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224602 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224602