Added login screen mode for adding users into session.

chrome/browser/chromeos/login/user_adding_screen.h

Index: chrome/browser/chromeos/login/user_adding_screen.h
diff --git a/chrome/browser/chromeos/login/user_adding_screen.h b/chrome/browser/chromeos/login/user_adding_screen.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4bdc09d6b8fd0166fedd599d7d3e700b23fcb07
--- /dev/null
+++ b/chrome/browser/chromeos/login/user_adding_screen.h
@@ -0,0 +1,42 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_CHROMEOS_LOGIN_USER_ADDING_SCREEN_H_
+#define CHROME_BROWSER_CHROMEOS_LOGIN_USER_ADDING_SCREEN_H_
+
+#include "base/basictypes.h"
+
+namespace chromeos {
+
+// An interface that defines screen for adding users into multi-profile session.
+// Current implementation is a singleton.
+// TODO(dzhioev): get rid of singleton.
+class UserAddingScreen {
+ public:
+  struct Observer {
+    virtual void OnUserAddingStarted() {}
+    virtual void OnUserAddingFinished() {}
+    virtual ~Observer() {}
+  };
+
+  static UserAddingScreen* Get();
+
+  virtual void Start() = 0;
+  virtual void Cancel() = 0;
+  virtual bool IsRunning() = 0;
+
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
+
+ protected:
+  UserAddingScreen();
+  virtual ~UserAddingScreen();
+
+  DISALLOW_COPY_AND_ASSIGN(UserAddingScreen);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_LOGIN_USER_ADDING_SCREEN_H_
+