telepathyClient: Use protocol-specific policy

Since commit 79c04c93e4, we launch Polari instead of Empathy when
activating a chat notification for an IRC channel. It therefore makes
sense to follow Polari's notification policy for those notifications
rather than Empathy's.

https://bugzilla.gnome.org/show_bug.cgi?id=752881

js/ui/components/telepathyClient.js

@@ -303,6 +303,8 @@ const ChatSource = new Lang.Class({
     },
 
     _createPolicy: function() {
+        if (this._account.protocol_name == 'irc')
+            return new MessageTray.NotificationApplicationPolicy('org.gnome.Polari');
         return new MessageTray.NotificationApplicationPolicy('empathy');
     },