Add a method to LoginUIService to open the sign in UI in a popup.

chrome/browser/ui/webui/signin/login_ui_service.cc

Index: chrome/browser/ui/webui/signin/login_ui_service.cc
===================================================================
--- chrome/browser/ui/webui/signin/login_ui_service.cc	(revision 145894)
+++ chrome/browser/ui/webui/signin/login_ui_service.cc	(working copy)
@@ -13,14 +13,27 @@
 
 LoginUIService::~LoginUIService() {}
 
+void LoginUIService::AddObserver(Observer* observer) {
+  observer_list_.AddObserver(observer);
+}
+
+void LoginUIService::RemoveObserver(Observer* observer) {
+  observer_list_.RemoveObserver(observer);
+}
+
 void LoginUIService::SetLoginUI(LoginUI* ui) {
   DCHECK(!current_login_ui() || current_login_ui() == ui);
   ui_ = ui;
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnLoginUIShown(ui_));
 }
 
 void LoginUIService::LoginUIClosed(LoginUI* ui) {
-  if (current_login_ui() == ui)
-    ui_ = NULL;
+  if (current_login_ui() != ui)
+    return;
+
+  LoginUI* ui = ui_;
+  ui_ = NULL;
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnLoginUIClosed(ui));
 }
 
 void LoginUIService::ShowLoginUI(Browser* browser) {