Removed old login screen from source.

chrome/browser/chromeos/login/existing_user_controller.cc

Index: chrome/browser/chromeos/login/existing_user_controller.cc
diff --git a/chrome/browser/chromeos/login/existing_user_controller.cc b/chrome/browser/chromeos/login/existing_user_controller.cc
index 9718534e801e930ef988fbfb8f3d6144019b9299..037f7cd44f7e3c88ffce127f12b6c47c9e2d906e 100644
--- a/chrome/browser/chromeos/login/existing_user_controller.cc
+++ b/chrome/browser/chromeos/login/existing_user_controller.cc
@@ -115,6 +115,8 @@ void EnableTooltipsIfNeeded(const std::vector<UserController*>& controllers) {
 
 ExistingUserController*
   ExistingUserController::delete_scheduled_instance_ = NULL;
+ExistingUserController*
+  ExistingUserController::current_controller_ = NULL;
 
 // TODO(xiyuan): Wait for the cached settings update before using them.
 ExistingUserController::ExistingUserController(
@@ -130,6 +132,8 @@ ExistingUserController::ExistingUserController(
       method_factory_(this) {
   if (delete_scheduled_instance_)
     delete_scheduled_instance_->Delete();
+  DCHECK(current_controller_ == NULL);
+  current_controller_ = this;
 
   // Caclulate the max number of users from available screen size.
   if (UserCrosSettingsProvider::cached_show_users_on_signin()) {
@@ -243,6 +247,8 @@ ExistingUserController::~ExistingUserController() {
   WmMessageListener::instance()->RemoveObserver(this);
 
   STLDeleteElements(&controllers_);
+  DCHECK(current_controller_ != NULL);
+  current_controller_ = NULL;
 }
 
 void ExistingUserController::Delete() {