Consolidate creation of login and unlock dialog in the screenshield

The design calls for the curtain to appear in the gdm greeter too.
Implement this by having the screenshield manage the login dialog
(delegating its creation to SessionMode).

https://bugzilla.gnome.org/show_bug.cgi?id=619955

js/ui/main.js

@@ -36,6 +36,7 @@ const SessionMode = imports.ui.sessionMode;
 const ShellDBus = imports.ui.shellDBus;
 const ShellMountOperation = imports.ui.shellMountOperation;
 const TelepathyClient = imports.ui.telepathyClient;
+const UnlockDialog = imports.ui.unlockDialog;
 const WindowManager = imports.ui.windowManager;
 const Magnifier = imports.ui.magnifier;
 const XdndHandler = imports.ui.xdndHandler;
@@ -94,14 +95,21 @@ function createUserSession() {
 }
 
 function createGDMSession() {
+    screenShield.showDialog();
+}
+
+function createGDMLoginDialog(parentActor) {
     // We do this this here instead of at the top to prevent GDM
     // related code from getting loaded in normal user sessions
     const LoginDialog = imports.gdm.loginDialog;
 
-    let loginDialog = new LoginDialog.LoginDialog();
-    loginDialog.connect('loaded', function() {
-                            loginDialog.open();
-                        });
+    let loginDialog = new LoginDialog.LoginDialog(parentActor);
+    return [loginDialog, true];
+}
+
+function createSessionUnlockDialog(parentActor) {
+    let dialog = new UnlockDialog.UnlockDialog(parentActor);
+    return [dialog, false];
 }
 
 function createInitialSetupSession() {