session_manager: Add SessionManagerObserver interface

components/session_manager/core/session_manager.cc

 // Copyright 2014 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 "components/session_manager/core/session_manager.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "build/build_config.h"
@@ skipping 13 matching lines @@
   DCHECK_EQ(instance, this);
   SessionManager::SetInstance(nullptr);
 }
 
 // static
 SessionManager* SessionManager::Get() {
   return SessionManager::instance;
 }
 
 void SessionManager::SetSessionState(SessionState state) {
+  if (session_state_ == state)
+    return;
+
   VLOG(1) << "Changing session state to: " << static_cast<int>(state);
 
-  if (session_state_ != state) {
-    // TODO(nkostylev): Notify observers about the state change.
-    // TODO(nkostylev): Add code to process session state change and probably
-    // replace delegate_ if needed.
-    session_state_ = state;
-  }
+  session_state_ = state;
+  for (auto* observer : observers_)
+    observer->OnSessionStateChanged();
 }
 
 void SessionManager::CreateSession(const AccountId& user_account_id,
                                    const std::string& user_id_hash) {
   CreateSessionInternal(user_account_id, user_id_hash,
                         false /* browser_restart */);
 }
 
 void SessionManager::CreateSessionForRestart(const AccountId& user_account_id,
                                              const std::string& user_id_hash) {
   CreateSessionInternal(user_account_id, user_id_hash,
                         true /* browser_restart */);
 }
 
 bool SessionManager::IsSessionStarted() const {
   return session_started_;
 }
 
 void SessionManager::SessionStarted() {
   session_started_ = true;
 }
 
+void SessionManager::AddObserver(SessionManagerObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void SessionManager::RemoveObserver(SessionManagerObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 void SessionManager::NotifyUserLoggedIn(const AccountId& user_account_id,
                                         const std::string& user_id_hash,
                                         bool browser_restart) {
   auto* user_manager = user_manager::UserManager::Get();
   if (!user_manager)
     return;
   user_manager->UserLoggedIn(user_account_id, user_id_hash, browser_restart);
 }
 
 // static
 void SessionManager::SetInstance(SessionManager* session_manager) {
   SessionManager::instance = session_manager;
 }
 
 void SessionManager::CreateSessionInternal(const AccountId& user_account_id,
                                            const std::string& user_id_hash,
                                            bool browser_restart) {
   DCHECK(std::find_if(sessions_.begin(), sessions_.end(),
                       [user_account_id](const Session& session) {
                         return session.user_account_id == user_account_id;
                       }) == sessions_.end());
 
   sessions_.push_back({next_id_++, user_account_id});
   NotifyUserLoggedIn(user_account_id, user_id_hash, browser_restart);
 }
 
 }  // namespace session_manager