Refactoring ash::SystemTrayDelegate: extracting Clock-related stuff.

SystemTrayDelegate has become a bit of a dumping ground. This CL moves all
Clock-related stuff from systemTrayDelegateChromeOS to new object
chromeos::system::SystemClock .

BUG=513120
TEST=manual

Review URL: https://codereview.chromium.org/1261903005

Cr-Commit-Position: refs/heads/master@{#343178}

12 files changed, 384 insertions, 133 deletions

diff --git a/ash/system/tray/system_tray_delegate.cc b/ash/system/tray/system_tray_delegate.cc
index 1cfb5e5..022ee4e 100644
--- a/ash/system/tray/system_tray_delegate.cc
+++ b/ash/system/tray/system_tray_delegate.cc
@@ -4,8 +4,6 @@
 
 #include "ash/system/tray/system_tray_delegate.h"
 
-#include "base/logging.h"
-
 namespace ash {
 
 NetworkIconInfo::NetworkIconInfo()
@@ -289,8 +287,4 @@ VPNDelegate* SystemTrayDelegate::GetVPNDelegate() const {
   return nullptr;
 }
 
-void SystemTrayDelegate::SetLastFocusedPodHourClockType(
-    base::HourClockType user_hour_clock_type) {
-}
-
 }  // namespace ash
diff --git a/ash/system/tray/system_tray_delegate.h b/ash/system/tray/system_tray_delegate.h
index be1c96c..cd1ee8b 100644
--- a/ash/system/tray/system_tray_delegate.h
+++ b/ash/system/tray/system_tray_delegate.h
@@ -337,12 +337,6 @@ class ASH_EXPORT SystemTrayDelegate {
 
   // Returns VPNDelegate. May return nullptr.
   virtual VPNDelegate* GetVPNDelegate() const;
-
-  // For ChromeOS login screen updates focused POD clock type.
-  // TODO (alemate): Move all clock-related stuff to a separate file.
-  // See https://crbug.com/513120 .
-  virtual void SetLastFocusedPodHourClockType(
-      base::HourClockType hour_clock_type);
 };
 
 }  // namespace ash
diff --git a/chrome/browser/browser_process_platform_part_chromeos.cc b/chrome/browser/browser_process_platform_part_chromeos.cc
index 978db1a..4ee4608 100644
--- a/chrome/browser/browser_process_platform_part_chromeos.cc
+++ b/chrome/browser/browser_process_platform_part_chromeos.cc
@@ -18,6 +18,7 @@
 #include "chrome/browser/chromeos/system/automatic_reboot_manager.h"
 #include "chrome/browser/chromeos/system/device_disabling_manager.h"
 #include "chrome/browser/chromeos/system/device_disabling_manager_default_delegate.h"
+#include "chrome/browser/chromeos/system/system_clock.h"
 #include "chrome/browser/chromeos/system/timezone_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_switches.h"
@@ -126,6 +127,12 @@ chromeos::TimeZoneResolver* BrowserProcessPlatformPart::GetTimezoneResolver() {
   return timezone_resolver_.get();
 }
 
+chromeos::system::SystemClock* BrowserProcessPlatformPart::GetSystemClock() {
+  if (!system_clock_.get())
+    system_clock_.reset(new chromeos::system::SystemClock());
+
+  return system_clock_.get();
+}
 void BrowserProcessPlatformPart::StartTearDown() {
   // interactive_ui_tests check for memory leaks before this object is
   // destroyed.  So we need to destroy |timezone_resolver_| here.
diff --git a/chrome/browser/browser_process_platform_part_chromeos.h b/chrome/browser/browser_process_platform_part_chromeos.h
index a06cbbc..a067b51 100644
--- a/chrome/browser/browser_process_platform_part_chromeos.h
+++ b/chrome/browser/browser_process_platform_part_chromeos.h
@@ -25,6 +25,7 @@ namespace system {
 class AutomaticRebootManager;
 class DeviceDisablingManager;
 class DeviceDisablingManagerDefaultDelegate;
+class SystemClock;
 }
 }
 
@@ -94,6 +95,8 @@ class BrowserProcessPlatformPart : public BrowserProcessPlatformPartBase,
   scoped_ptr<policy::BrowserPolicyConnector> CreateBrowserPolicyConnector()
       override;
 
+  chromeos::system::SystemClock* GetSystemClock();
+
  private:
   void CreateProfileHelper();
 
@@ -114,6 +117,8 @@ class BrowserProcessPlatformPart : public BrowserProcessPlatformPartBase,
 
   scoped_ptr<chromeos::TimeZoneResolver> timezone_resolver_;
 
+  scoped_ptr<chromeos::system::SystemClock> system_clock_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserProcessPlatformPart);
 };
 
diff --git a/chrome/browser/chromeos/system/system_clock.cc b/chrome/browser/chromeos/system/system_clock.cc
new file mode 100644
index 0000000..2b3fdc8
--- /dev/null
+++ b/chrome/browser/chromeos/system/system_clock.cc
@@ -0,0 +1,219 @@
+// Copyright 2015 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 "chrome/browser/chromeos/system/system_clock.h"
+
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/prefs/pref_change_registrar.h"
+#include "base/prefs/pref_service.h"
+#include "chrome/browser/chrome_notification_types.h"
+#include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h"
+#include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos_factory.h"
+#include "chrome/browser/chromeos/profiles/profile_helper.h"
+#include "chrome/browser/chromeos/settings/cros_settings.h"
+#include "chrome/browser/chromeos/system/system_clock_observer.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/common/pref_names.h"
+#include "chromeos/login/login_state.h"
+#include "chromeos/settings/cros_settings_names.h"
+#include "components/user_manager/user.h"
+#include "components/user_manager/user_manager.h"
+#include "content/public/browser/notification_service.h"
+
+namespace chromeos {
+namespace system {
+
+namespace {
+
+void SetShouldUse24HourClock(bool use_24_hour_clock) {
+  user_manager::User* const user =
+      user_manager::UserManager::Get()->GetActiveUser();
+  CHECK(user);
+  Profile* const profile = ProfileHelper::Get()->GetProfileByUser(user);
+  if (!profile)
+    return;  // May occur in tests or if not running on a device.
+  OwnerSettingsServiceChromeOS* const service =
+      OwnerSettingsServiceChromeOSFactory::GetForBrowserContext(profile);
+  CHECK(service);
+  service->SetBoolean(kSystemUse24HourClock, use_24_hour_clock);
+}
+
+}  // anonymous namespace
+
+SystemClock::SystemClock()
+    : user_pod_was_focused_(false),
+      last_focused_pod_hour_clock_type_(base::k12HourClock),
+      user_profile_(NULL),
+      device_settings_observer_(CrosSettings::Get()->AddSettingsObserver(
+          kSystemUse24HourClock,
+          base::Bind(&SystemClock::OnSystemPrefChanged,
+                     base::Unretained(this)))) {
+  if (LoginState::IsInitialized())
+    LoginState::Get()->AddObserver(this);
+  // Register notifications on construction so that events such as
+  // PROFILE_CREATED do not get missed if they happen before Initialize().
+  registrar_.reset(new content::NotificationRegistrar);
+  if (!LoginState::IsInitialized() ||
+      LoginState::Get()->GetLoggedInUserType() ==
+          LoginState::LOGGED_IN_USER_NONE) {
+    registrar_->Add(this, chrome::NOTIFICATION_SESSION_STARTED,
+                    content::NotificationService::AllSources());
+  }
+  registrar_->Add(this, chrome::NOTIFICATION_PROFILE_CREATED,
+                  content::NotificationService::AllSources());
+  registrar_->Add(this, chrome::NOTIFICATION_PROFILE_DESTROYED,
+                  content::NotificationService::AllSources());
+  registrar_->Add(this, chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED,
+                  content::NotificationService::AllSources());
+  user_manager::UserManager::Get()->AddSessionStateObserver(this);
+}
+
+SystemClock::~SystemClock() {
+  registrar_.reset();
+  device_settings_observer_.reset();
+  if (LoginState::IsInitialized())
+    LoginState::Get()->RemoveObserver(this);
+  if (user_manager::UserManager::IsInitialized())
+    user_manager::UserManager::Get()->RemoveSessionStateObserver(this);
+}
+
+// LoginState::Observer overrides.
+void SystemClock::LoggedInStateChanged() {
+  // It apparently sometimes takes a while after login before the current user
+  // is recognized as the owner. Make sure that the system-wide clock setting
+  // is updated when the recognition eventually happens (crbug.com/278601).
+  if (user_manager::UserManager::Get()->IsCurrentUserOwner())
+    SetShouldUse24HourClock(ShouldUse24HourClock());
+}
+
+// content::NotificationObserver implementation.
+void SystemClock::Observe(int type,
+                          const content::NotificationSource& source,
+                          const content::NotificationDetails& details) {
+  switch (type) {
+    case chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED: {
+      UpdateClockType();
+      break;
+    }
+    case chrome::NOTIFICATION_PROFILE_CREATED: {
+      OnActiveProfileChanged(content::Source<Profile>(source).ptr());
+      registrar_->Remove(this, chrome::NOTIFICATION_PROFILE_CREATED,
+                         content::NotificationService::AllSources());
+      break;
+    }
+    case chrome::NOTIFICATION_PROFILE_DESTROYED: {
+      if (OnProfileDestroyed(content::Source<Profile>(source).ptr())) {
+        registrar_->Remove(this, chrome::NOTIFICATION_PROFILE_DESTROYED,
+                           content::NotificationService::AllSources());
+      }
+      break;
+    }
+    case chrome::NOTIFICATION_SESSION_STARTED: {
+      OnActiveProfileChanged(ProfileManager::GetActiveUserProfile());
+      break;
+    }
+    default:
+      NOTREACHED();
+  }
+}
+
+void SystemClock::ActiveUserChanged(const user_manager::User* /*user*/) {
+  UpdateClockType();
+}
+
+void SystemClock::AddObserver(SystemClockObserver* observer) {
+  observer_list_.AddObserver(observer);
+}
+
+void SystemClock::RemoveObserver(SystemClockObserver* observer) {
+  observer_list_.RemoveObserver(observer);
+}
+
+void SystemClock::OnActiveProfileChanged(Profile* profile) {
+  user_profile_ = profile;
+  PrefService* prefs = profile->GetPrefs();
+  user_pref_registrar_.reset(new PrefChangeRegistrar);
+  user_pref_registrar_->Init(prefs);
+  user_pref_registrar_->Add(
+      prefs::kUse24HourClock,
+      base::Bind(&SystemClock::UpdateClockType, base::Unretained(this)));
+}
+
+bool SystemClock::OnProfileDestroyed(Profile* profile) {
+  if (profile != user_profile_)
+    return false;
+  user_pref_registrar_.reset();
+  user_profile_ = NULL;
+  return true;
+}
+
+void SystemClock::SetLastFocusedPodHourClockType(
+    base::HourClockType hour_clock_type) {
+  user_pod_was_focused_ = true;
+  last_focused_pod_hour_clock_type_ = hour_clock_type;
+  UpdateClockType();
+}
+
+bool SystemClock::ShouldUse24HourClock() const {
+  // On login screen and in guest mode owner default is used for
+  // kUse24HourClock preference.
+  const chromeos::LoginState::LoggedInUserType status =
+      LoginState::IsInitialized() ? LoginState::Get()->GetLoggedInUserType()
+                                  : LoginState::LOGGED_IN_USER_NONE;
+
+  if (status == LoginState::LOGGED_IN_USER_NONE && user_pod_was_focused_)
+    return last_focused_pod_hour_clock_type_ == base::k24HourClock;
+
+  const CrosSettings* const cros_settings = CrosSettings::Get();
+  bool system_use_24_hour_clock = true;
+  const bool system_value_found = cros_settings->GetBoolean(
+      kSystemUse24HourClock, &system_use_24_hour_clock);
+
+  if ((status == LoginState::LOGGED_IN_USER_NONE) || !user_pref_registrar_) {
+    return (system_value_found
+                ? system_use_24_hour_clock
+                : (base::GetHourClockType() == base::k24HourClock));
+  }
+
+  const PrefService::Preference* user_pref =
+      user_pref_registrar_->prefs()->FindPreference(prefs::kUse24HourClock);
+  if (status == LoginState::LOGGED_IN_USER_GUEST &&
+      user_pref->IsDefaultValue()) {
+    return (system_value_found
+                ? system_use_24_hour_clock
+                : (base::GetHourClockType() == base::k24HourClock));
+  }
+
+  user_manager::User* active_user =
+      user_manager::UserManager::Get()->GetActiveUser();
+  if (active_user) {
+    Profile* user_profile = ProfileHelper::Get()->GetProfileByUser(active_user);
+    if (user_profile) {
+      user_pref =
+          user_profile->GetPrefs()->FindPreference(prefs::kUse24HourClock);
+    }
+  }
+
+  bool use_24_hour_clock = true;
+  user_pref->GetValue()->GetAsBoolean(&use_24_hour_clock);
+  return use_24_hour_clock;
+}
+
+void SystemClock::OnSystemPrefChanged() {
+  UpdateClockType();
+}
+
+void SystemClock::UpdateClockType() {
+  // This also works for enterprise-managed devices because they never have
+  // a local owner.
+  if (user_manager::UserManager::Get()->IsCurrentUserOwner())
+    SetShouldUse24HourClock(ShouldUse24HourClock());
+  FOR_EACH_OBSERVER(SystemClockObserver, observer_list_,
+                    OnSystemClockChanged(this));
+}
+
+}  // namespace system
+}  // namespace chromeos
diff --git a/chrome/browser/chromeos/system/system_clock.h b/chrome/browser/chromeos/system/system_clock.h
new file mode 100644
index 0000000..f6a5d32
--- /dev/null
+++ b/chrome/browser/chromeos/system/system_clock.h
@@ -0,0 +1,89 @@
+// Copyright 2015 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_SYSTEM_SYSTEM_CLOCK_H_
+#define CHROME_BROWSER_CHROMEOS_SYSTEM_SYSTEM_CLOCK_H_
+
+#include "base/callback_list.h"
+#include "base/i18n/time_formatting.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "chromeos/login/login_state.h"
+#include "components/user_manager/user_manager.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+class Profile;
+class PrefChangeRegistrar;
+
+namespace user_manager {
+class User;
+}
+
+namespace chromeos {
+namespace system {
+
+class SystemClockObserver;
+
+// This is a global singleton (actually a member of BrowserProcessPlatformPart)
+// that is responsible for correct time formatting. It listens to events that
+// modify on-screen time representation (like ActiveUserChanged) and notifies
+// observers.
+//
+// (Most of) this code used to be a part of ash::SystemTrayDelegate.
+class SystemClock : public chromeos::LoginState::Observer,
+                    public content::NotificationObserver,
+                    public user_manager::UserManager::UserSessionStateObserver {
+ public:
+  SystemClock();
+  ~SystemClock() override;
+
+  void SetLastFocusedPodHourClockType(base::HourClockType hour_clock_type);
+
+  void AddObserver(SystemClockObserver* observer);
+  void RemoveObserver(SystemClockObserver* observer);
+
+  bool ShouldUse24HourClock() const;
+
+  // content::NotificationObserver implementation.
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+  // user_manager::UserManager::UserSessionStateObserver overrides
+  void ActiveUserChanged(const user_manager::User* user) override;
+
+ private:
+  // Should be the same as CrosSettings::ObserverSubscription.
+  typedef base::CallbackList<void(void)>::Subscription
+      CrosSettingsObserverSubscription;
+
+  void OnActiveProfileChanged(Profile* profile);
+  bool OnProfileDestroyed(Profile* profile);
+
+  // LoginState::Observer overrides.
+  void LoggedInStateChanged() override;
+
+  void OnSystemPrefChanged();
+
+  void UpdateClockType();
+
+  bool user_pod_was_focused_;
+  base::HourClockType last_focused_pod_hour_clock_type_;
+
+  Profile* user_profile_;
+  scoped_ptr<content::NotificationRegistrar> registrar_;
+  scoped_ptr<PrefChangeRegistrar> user_pref_registrar_;
+
+  base::ObserverList<SystemClockObserver> observer_list_;
+
+  scoped_ptr<CrosSettingsObserverSubscription> device_settings_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(SystemClock);
+};
+
+}  // namespace system
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_SYSTEM_CLOCK_H_
diff --git a/chrome/browser/chromeos/system/system_clock_observer.cc b/chrome/browser/chromeos/system/system_clock_observer.cc
new file mode 100644
index 0000000..52a8dc1
--- /dev/null
+++ b/chrome/browser/chromeos/system/system_clock_observer.cc
@@ -0,0 +1,14 @@
+// Copyright 2015 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 "chrome/browser/chromeos/system/system_clock_observer.h"
+
+namespace chromeos {
+namespace system {
+
+SystemClockObserver::~SystemClockObserver() {
+}
+
+}  // namespace system
+}  // namespace chromeos
diff --git a/chrome/browser/chromeos/system/system_clock_observer.h b/chrome/browser/chromeos/system/system_clock_observer.h
new file mode 100644
index 0000000..08f4494
--- /dev/null
+++ b/chrome/browser/chromeos/system/system_clock_observer.h
@@ -0,0 +1,25 @@
+// Copyright 2015 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_SYSTEM_SYSTEM_CLOCK_OBSERVER_H_
+#define CHROME_BROWSER_CHROMEOS_SYSTEM_SYSTEM_CLOCK_OBSERVER_H_
+
+#include "base/macros.h"
+
+namespace chromeos {
+namespace system {
+
+class SystemClock;
+
+// This is observer for chromeos::system::SystemClock .
+class SystemClockObserver {
+ public:
+  virtual ~SystemClockObserver();
+  virtual void OnSystemClockChanged(SystemClock*) = 0;
+};
+
+}  // namespace system
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_SYSTEM_CLOCK_OBSERVER_H_
diff --git a/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc b/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
index 31c4c04..4f80cb6 100644
--- a/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
+++ b/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
@@ -58,8 +58,6 @@
 #include "chrome/browser/chromeos/login/users/chrome_user_manager.h"
 #include "chrome/browser/chromeos/login/users/supervised_user_manager.h"
 #include "chrome/browser/chromeos/options/network_config_view.h"
-#include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos.h"
-#include "chrome/browser/chromeos/ownership/owner_settings_service_chromeos_factory.h"
 #include "chrome/browser/chromeos/policy/browser_policy_connector_chromeos.h"
 #include "chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h"
 #include "chrome/browser/chromeos/profiles/multiprofiles_intro_dialog.h"
@@ -180,19 +178,6 @@ void OnAcceptMultiprofilesIntro(bool no_show_again) {
   UserAddingScreen::Get()->Start();
 }
 
-void SetShouldUse24HourClock(bool use_24_hour_clock) {
-  user_manager::User* const user =
-      user_manager::UserManager::Get()->GetActiveUser();
-  CHECK(user);
-  Profile* const profile = ProfileHelper::Get()->GetProfileByUser(user);
-  if (!profile)
-    return;  // May occur in tests or if not running on a device.
-  OwnerSettingsServiceChromeOS* const service =
-      OwnerSettingsServiceChromeOSFactory::GetForBrowserContext(profile);
-  CHECK(service);
-  service->SetBoolean(kSystemUse24HourClock, use_24_hour_clock);
-}
-
 }  // namespace
 
 SystemTrayDelegateChromeOS::SystemTrayDelegateChromeOS()
@@ -207,13 +192,7 @@ SystemTrayDelegateChromeOS::SystemTrayDelegateChromeOS()
       cast_config_delegate_(new CastConfigDelegateChromeos()),
       networking_config_delegate_(new NetworkingConfigDelegateChromeos()),
       volume_control_delegate_(new VolumeController()),
-      device_settings_observer_(CrosSettings::Get()->AddSettingsObserver(
-          kSystemUse24HourClock,
-          base::Bind(&SystemTrayDelegateChromeOS::UpdateClockType,
-                     base::Unretained(this)))),
       vpn_delegate_(new VPNDelegateChromeOS),
-      user_pod_was_focused_(false),
-      last_focused_pod_hour_clock_type_(base::k12HourClock),
       weak_ptr_factory_(this) {
   // Register notifications on construction so that events such as
   // PROFILE_CREATED do not get missed if they happen before Initialize().
@@ -235,8 +214,6 @@ SystemTrayDelegateChromeOS::SystemTrayDelegateChromeOS()
   registrar_->Add(this,
                   chrome::NOTIFICATION_PROFILE_DESTROYED,
                   content::NotificationService::AllSources());
-  registrar_->Add(this, chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED,
-                  content::NotificationService::AllSources());
 
   AccessibilityManager* accessibility_manager = AccessibilityManager::Get();
   CHECK(accessibility_manager);
@@ -254,7 +231,10 @@ void SystemTrayDelegateChromeOS::Initialize() {
 
   input_method::InputMethodManager::Get()->AddObserver(this);
   ui::ime::InputMethodMenuManager::GetInstance()->AddObserver(this);
-  UpdateClockType();
+
+  g_browser_process->platform_part()->GetSystemClock()->AddObserver(this);
+
+  OnSystemClockChanged(g_browser_process->platform_part()->GetSystemClock());
 
   device::BluetoothAdapterFactory::GetAdapter(
       base::Bind(&SystemTrayDelegateChromeOS::InitializeOnAdapterReady,
@@ -263,9 +243,6 @@ void SystemTrayDelegateChromeOS::Initialize() {
   ash::Shell::GetInstance()->session_state_delegate()->AddSessionStateObserver(
       this);
 
-  if (LoginState::IsInitialized())
-    LoginState::Get()->AddObserver(this);
-
   if (CrasAudioHandler::IsInitialized())
     CrasAudioHandler::Get()->AddAudioObserver(this);
 
@@ -273,7 +250,6 @@ void SystemTrayDelegateChromeOS::Initialize() {
 }
 
 void SystemTrayDelegateChromeOS::Shutdown() {
-  device_settings_observer_.reset();
 }
 
 void SystemTrayDelegateChromeOS::InitializeOnAdapterReady(
@@ -317,6 +293,7 @@ SystemTrayDelegateChromeOS::~SystemTrayDelegateChromeOS() {
   // Unregister a11y status subscription.
   accessibility_subscription_.reset();
 
+  g_browser_process->platform_part()->GetSystemClock()->RemoveObserver(this);
   DBusThreadManager::Get()->GetSessionManagerClient()->RemoveObserver(this);
   input_method::InputMethodManager::Get()->RemoveObserver(this);
   ui::ime::InputMethodMenuManager::GetInstance()->RemoveObserver(this);
@@ -324,7 +301,6 @@ SystemTrayDelegateChromeOS::~SystemTrayDelegateChromeOS() {
   ash::Shell::GetInstance()
       ->session_state_delegate()
       ->RemoveSessionStateObserver(this);
-  LoginState::Get()->RemoveObserver(this);
 
   if (CrasAudioHandler::IsInitialized())
     CrasAudioHandler::Get()->RemoveAudioObserver(this);
@@ -934,10 +910,6 @@ void SystemTrayDelegateChromeOS::SetProfile(Profile* profile) {
   user_pref_registrar_.reset(new PrefChangeRegistrar);
   user_pref_registrar_->Init(prefs);
   user_pref_registrar_->Add(
-      prefs::kUse24HourClock,
-      base::Bind(&SystemTrayDelegateChromeOS::UpdateClockType,
-                 base::Unretained(this)));
-  user_pref_registrar_->Add(
       prefs::kLanguageRemapSearchKeyTo,
       base::Bind(&SystemTrayDelegateChromeOS::OnLanguageRemapSearchKeyToChanged,
                  base::Unretained(this)));
@@ -986,64 +958,16 @@ bool SystemTrayDelegateChromeOS::UnsetProfile(Profile* profile) {
 }
 
 bool SystemTrayDelegateChromeOS::GetShouldUse24HourClockForTesting() const {
-  return ShouldUse24HourClock();
-}
-
-void SystemTrayDelegateChromeOS::SetLastFocusedPodHourClockType(
-    base::HourClockType user_hour_clock_type) {
-  user_pod_was_focused_ = true;
-  last_focused_pod_hour_clock_type_ = user_hour_clock_type;
-  UpdateClockType();
-}
-
-bool SystemTrayDelegateChromeOS::ShouldUse24HourClock() const {
-  // On login screen and in guest mode owner default is used for
-  // kUse24HourClock preference.
-  const ash::user::LoginStatus status = GetUserLoginStatus();
-
-  if (status == ash::user::LOGGED_IN_NONE && user_pod_was_focused_)
-    return last_focused_pod_hour_clock_type_ == base::k24HourClock;
-
-  const CrosSettings* const cros_settings = CrosSettings::Get();
-  bool system_use_24_hour_clock = true;
-  const bool system_value_found = cros_settings->GetBoolean(
-      kSystemUse24HourClock, &system_use_24_hour_clock);
-
-  if ((status == ash::user::LOGGED_IN_NONE) || !user_pref_registrar_)
-    return (system_value_found
-                ? system_use_24_hour_clock
-                : (base::GetHourClockType() == base::k24HourClock));
-
-  const PrefService::Preference* user_pref =
-      user_pref_registrar_->prefs()->FindPreference(prefs::kUse24HourClock);
-  if (status == ash::user::LOGGED_IN_GUEST && user_pref->IsDefaultValue())
-    return (system_value_found
-                ? system_use_24_hour_clock
-                : (base::GetHourClockType() == base::k24HourClock));
-
-  user_manager::User* active_user =
-      user_manager::UserManager::Get()->GetActiveUser();
-  if (active_user) {
-    Profile* user_profile = ProfileHelper::Get()->GetProfileByUser(active_user);
-    if (user_profile) {
-      user_pref =
-          user_profile->GetPrefs()->FindPreference(prefs::kUse24HourClock);
-    }
-  }
-
-  bool use_24_hour_clock = true;
-  user_pref->GetValue()->GetAsBoolean(&use_24_hour_clock);
-  return use_24_hour_clock;
+  return g_browser_process->platform_part()
+      ->GetSystemClock()
+      ->ShouldUse24HourClock();
 }
 
-void SystemTrayDelegateChromeOS::UpdateClockType() {
-  const bool use_24_hour_clock = ShouldUse24HourClock();
+void SystemTrayDelegateChromeOS::OnSystemClockChanged(
+    system::SystemClock* system_clock) {
+  const bool use_24_hour_clock = system_clock->ShouldUse24HourClock();
   clock_type_ = use_24_hour_clock ? base::k24HourClock : base::k12HourClock;
   GetSystemTrayNotifier()->NotifyDateFormatChanged();
-  // This also works for enterprise-managed devices because they never have
-  // local owner.
-  if (user_manager::UserManager::Get()->IsCurrentUserOwner())
-    SetShouldUse24HourClock(use_24_hour_clock);
 }
 
 void SystemTrayDelegateChromeOS::UpdateShowLogoutButtonInTray() {
@@ -1132,15 +1056,6 @@ void SystemTrayDelegateChromeOS::NotifyIfLastWindowClosed() {
   GetSystemTrayNotifier()->NotifyLastWindowClosed();
 }
 
-// LoginState::Observer overrides.
-void SystemTrayDelegateChromeOS::LoggedInStateChanged() {
-  // It apparently sometimes takes a while after login before the current user
-  // is recognized as the owner. Make sure that the system-wide clock setting
-  // is updated when the recognition eventually happens (crbug.com/278601).
-  if (user_manager::UserManager::Get()->IsCurrentUserOwner())
-    SetShouldUse24HourClock(ShouldUse24HourClock());
-}
-
 // Overridden from SessionManagerClient::Observer.
 void SystemTrayDelegateChromeOS::ScreenIsLocked() {
   screen_locked_ = true;
@@ -1165,10 +1080,6 @@ void SystemTrayDelegateChromeOS::Observe(
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   switch (type) {
-    case chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED: {
-      UpdateClockType();
-      break;
-    }
     case chrome::NOTIFICATION_UPGRADE_RECOMMENDED: {
       ash::UpdateInfo info;
       GetUpdateInfo(content::Source<UpgradeDetector>(source).ptr(), &info);
@@ -1348,7 +1259,6 @@ void SystemTrayDelegateChromeOS::UserAddedToSession(
 
 void SystemTrayDelegateChromeOS::ActiveUserChanged(
     const std::string& /* user_id */) {
-  UpdateClockType();
 }
 
 // Overridden from chrome::BrowserListObserver.
diff --git a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
index c1c193d..58f93a8 100644
--- a/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
+++ b/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
@@ -23,12 +23,13 @@
 #include "base/prefs/pref_change_registrar.h"
 #include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
 #include "chrome/browser/chromeos/settings/shutdown_policy_handler.h"
+#include "chrome/browser/chromeos/system/system_clock.h"
+#include "chrome/browser/chromeos/system/system_clock_observer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/supervised_user/supervised_user_service_observer.h"
 #include "chrome/browser/ui/browser_list_observer.h"
 #include "chromeos/audio/cras_audio_handler.h"
 #include "chromeos/dbus/session_manager_client.h"
-#include "chromeos/login/login_state.h"
 #include "components/policy/core/common/cloud/cloud_policy_store.h"
 #include "components/user_manager/user_manager.h"
 #include "content/public/browser/notification_observer.h"
@@ -55,7 +56,6 @@ class SystemTrayDelegateChromeOS
       public SessionManagerClient::Observer,
       public content::NotificationObserver,
       public input_method::InputMethodManager::Observer,
-      public chromeos::LoginState::Observer,
       public chromeos::CrasAudioHandler::AudioObserver,
       public device::BluetoothAdapter::Observer,
       public policy::CloudPolicyStore::Observer,
@@ -64,7 +64,8 @@ class SystemTrayDelegateChromeOS
       public extensions::AppWindowRegistry::Observer,
       public user_manager::UserManager::UserSessionStateObserver,
       public SupervisedUserServiceObserver,
-      public ShutdownPolicyHandler::Delegate  {
+      public ShutdownPolicyHandler::Delegate,
+      public system::SystemClockObserver {
  public:
   SystemTrayDelegateChromeOS();
 
@@ -147,8 +148,6 @@ class SystemTrayDelegateChromeOS
   void ShouldRebootOnShutdown(
       const ash::RebootOnShutdownCallback& callback) override;
   ash::VPNDelegate* GetVPNDelegate() const override;
-  void SetLastFocusedPodHourClockType(
-      base::HourClockType hour_clock_type) override;
 
   // Overridden from user_manager::UserManager::UserSessionStateObserver:
   void UserAddedToSession(const user_manager::User* active_user) override;
@@ -159,10 +158,10 @@ class SystemTrayDelegateChromeOS
   // browser tests need to call ShouldUse24HourClock().
   bool GetShouldUse24HourClockForTesting() const;
 
+  // chromeos::system::SystemClockObserver implementation.
+  void OnSystemClockChanged(system::SystemClock*) override;
+
  private:
-  // Should be the same as CrosSettings::ObserverSubscription.
-  typedef base::CallbackList<void(void)>::Subscription
-      CrosSettingsObserverSubscription;
 
   ash::SystemTray* GetPrimarySystemTray();
 
@@ -174,8 +173,6 @@ class SystemTrayDelegateChromeOS
 
   bool ShouldUse24HourClock() const;
 
-  void UpdateClockType();
-
   void UpdateShowLogoutButtonInTray();
 
   void UpdateLogoutDialogDuration();
@@ -192,9 +189,6 @@ class SystemTrayDelegateChromeOS
   // windows.
   void NotifyIfLastWindowClosed();
 
-  // LoginState::Observer overrides.
-  void LoggedInStateChanged() override;
-
   // Overridden from SessionManagerClient::Observer.
   void ScreenIsLocked() override;
   void ScreenIsUnlocked() override;
@@ -297,7 +291,6 @@ class SystemTrayDelegateChromeOS
   scoped_ptr<ash::CastConfigDelegate> cast_config_delegate_;
   scoped_ptr<ash::NetworkingConfigDelegate> networking_config_delegate_;
   scoped_ptr<ash::VolumeControlDelegate> volume_control_delegate_;
-  scoped_ptr<CrosSettingsObserverSubscription> device_settings_observer_;
   scoped_ptr<AccessibilityStatusSubscription> accessibility_subscription_;
   base::ScopedPtrHashMap<std::string,
                          scoped_ptr<ash::tray::UserAccountsDelegate>>
@@ -310,9 +303,6 @@ class SystemTrayDelegateChromeOS
 
   base::ObserverList<ash::ShutdownPolicyObserver> shutdown_policy_observers_;
 
-  bool user_pod_was_focused_;
-  base::HourClockType last_focused_pod_hour_clock_type_;
-
   base::WeakPtrFactory<SystemTrayDelegateChromeOS> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayDelegateChromeOS);
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
index 31c06b6..6465c61 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -9,7 +9,6 @@
 
 #include "ash/shell.h"
 #include "ash/system/chromeos/devicetype_utils.h"
-#include "ash/system/tray/system_tray_delegate.h"
 #include "ash/wm/lock_state_controller.h"
 #include "base/bind.h"
 #include "base/location.h"
@@ -49,6 +48,7 @@
 #include "chrome/browser/chromeos/policy/device_local_account.h"
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/chromeos/settings/cros_settings.h"
+#include "chrome/browser/chromeos/system/system_clock.h"
 #include "chrome/browser/io_thread.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_metrics.h"
@@ -1285,8 +1285,8 @@ void SigninScreenHandler::HandleFocusPod(const std::string& user_id) {
   bool use_24hour_clock = false;
   if (user_manager::UserManager::Get()->GetKnownUserBooleanPref(
           user_id, prefs::kUse24HourClock, &use_24hour_clock)) {
-    ash::Shell::GetInstance()
-        ->system_tray_delegate()
+    g_browser_process->platform_part()
+        ->GetSystemClock()
         ->SetLastFocusedPodHourClockType(use_24hour_clock ? base::k24HourClock
                                                           : base::k12HourClock);
   }
diff --git a/chrome/chrome_browser_chromeos.gypi b/chrome/chrome_browser_chromeos.gypi
index 2fc7cc6..9833ab8 100644
--- a/chrome/chrome_browser_chromeos.gypi
+++ b/chrome/chrome_browser_chromeos.gypi
@@ -995,6 +995,10 @@
         'browser/chromeos/system/input_device_settings_impl_x11.cc',
         'browser/chromeos/system/pointer_device_observer.cc',
         'browser/chromeos/system/pointer_device_observer.h',
+        'browser/chromeos/system/system_clock.cc',
+        'browser/chromeos/system/system_clock.h',
+        'browser/chromeos/system/system_clock_observer.cc',
+        'browser/chromeos/system/system_clock_observer.h',
         'browser/chromeos/system/timezone_util.cc',
         'browser/chromeos/system/timezone_util.h',
         'browser/chromeos/system_logs/command_line_log_source.cc',