endSessionDialog: Add logout/shutdown dialog

This commit adds a dialog for gnome-session to
privately use when initiating log outs and shut
downs.

Coordination is done over the bus.

https://bugzilla.gnome.org/show_bug.cgi?id=637187

js/ui/main.js

@@ -22,6 +22,7 @@ const _ = Gettext.gettext;
 
 const Chrome = imports.ui.chrome;
 const CtrlAltTab = imports.ui.ctrlAltTab;
+const EndSessionDialog = imports.ui.endSessionDialog;
 const Environment = imports.ui.environment;
 const ExtensionSystem = imports.ui.extensionSystem;
 const MessageTray = imports.ui.messageTray;
@@ -171,6 +172,10 @@ function start() {
         }
     });
 
+    // Provide the bus object for gnome-session to
+    // initiate logouts.
+    EndSessionDialog.init();
+
     global.gdk_screen.connect('monitors-changed', _relayout);
 
     ExtensionSystem.init();