ash: Fix system tray avatar not updated regression

ash/common/session/session_controller.cc

 // Copyright 2016 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.
 
 #include "ash/common/session/session_controller.h"
 
 #include <algorithm>
 
 #include "ash/common/login_status.h"
 #include "ash/common/session/session_state_observer.h"
@@ skipping 156 matching lines @@
       std::find_if(user_sessions_.begin(), user_sessions_.end(),
                    [&user_session](const mojom::UserSessionPtr& session) {
                      return session->session_id == user_session->session_id;
                    });
   if (it == user_sessions_.end()) {
     AddUserSession(std::move(user_session));
     return;
   }
 
   *it = std::move(user_session);
-  // TODO(xiyuan): Notify observers about meta change to replace things such as
-  //     NOTIFICATION_LOGIN_USER_IMAGE_CHANGED. http://crbug.com/670422
+  for (auto& observer : observers_)
+    observer.UserSessionUpdated((*it)->account_id);
 }
 
 void SessionController::SetUserSessionOrder(
     const std::vector<uint32_t>& user_session_order) {
   DCHECK_EQ(user_sessions_.size(), user_session_order.size());
 
   // Adjusts |user_sessions_| to match the given order.
   std::vector<mojom::UserSessionPtr> sessions;
   for (const auto& session_id : user_session_order) {
     auto it =
@@ skipping 78 matching lines @@
     case user_manager::NUM_USER_TYPES:
       // Avoid having a "default" case so the compiler catches new enum values.
       NOTREACHED();
       return LoginStatus::USER;
   }
   NOTREACHED();
   return LoginStatus::USER;
 }
 
 }  // namespace ash