Add SessionStateObserver with ActiveUserChanged()

chrome/browser/chromeos/login/user_manager.h

 // Copyright (c) 2012 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_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_USER_MANAGER_H_
 
 #include <string>
 
 #include "chrome/browser/chromeos/login/user.h"
@@ skipping 31 matching lines @@
     // Called when merge session state is changed.
     virtual void MergeSessionStateChanged(MergeSessionState state) {}
 
    protected:
     virtual ~Observer();
   };
 
   // TODO(nkostylev): Merge with session state refactoring CL.
   class UserSessionStateObserver {
    public:
+    // Called when active user has changed.
+    virtual void ActiveUserChanged(const User* active_user) {}
+
     // Called right before notifying on user change so that those who rely
     // on user_id hash would be accessing up-to-date value.
-    virtual void ActiveUserHashChanged(const std::string& hash) = 0;
+    virtual void ActiveUserHashChanged(const std::string& hash) {}
 
     // Called when UserManager finishes restoring user sessions after crash.
-    virtual void PendingUserSessionsRestoreFinished() = 0;
+    virtual void PendingUserSessionsRestoreFinished() {}
 
    protected:
     virtual ~UserSessionStateObserver();
   };
 
   // Username for stub login when not running on ChromeOS.
   static const char kStubUser[];
 
   // Magic e-mail addresses are bad. They exist here because some code already
   // depends on them and it is hard to figure out what. Any user types added in
@@ skipping 307 matching lines @@
   ScopedTestUserManager();
   ~ScopedTestUserManager();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScopedTestUserManager);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_USER_MANAGER_H_