Propagate User App Model ID to Tray Icon

This PR prevents dozens of items showing up in the notification area
preferences when using Squirrel for Windows, by ensuring that
notification tray items are tied to the User App Model ID.

atom/browser/ui/win/notify_icon.h

@@ -75,6 +75,9 @@ class NotifyIcon : public TrayIcon {
 
   // The context menu.
   ui::SimpleMenuModel* menu_model_;
+  
+  // A hash of the app model ID
+  GUID tray_app_id_hash_;
 
   DISALLOW_COPY_AND_ASSIGN(NotifyIcon);
 };