MD Settings: Show "Set date and time" button when relevant

chrome/browser/ui/webui/settings/chromeos/date_time_handler.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DATE_TIME_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DATE_TIME_HANDLER_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
+#include "chromeos/dbus/system_clock_client.h"
 #include "components/prefs/pref_change_registrar.h"
 
 namespace base {
 class ListValue;
 }
 
 namespace content {
 class WebUIDataSource;
 }
 
 namespace chromeos {
 namespace settings {
 
 // Chrome OS date and time settings page UI handler.
-class DateTimeHandler : public ::settings::SettingsPageUIHandler {
+class DateTimeHandler : public ::settings::SettingsPageUIHandler,
+                        public SystemClockClient::Observer {
  public:
   ~DateTimeHandler() override;
 
   // Adds load-time values to html_source before creating the handler.
   static DateTimeHandler* Create(content::WebUIDataSource* html_source);
 
   // SettingsPageUIHandler implementation.
   void RegisterMessages() override;
   void OnJavascriptAllowed() override;
   void OnJavascriptDisallowed() override;
 
  private:
   DateTimeHandler();
 
+  // SystemClockClient::Observer implementation.
+  void SystemClockCanSetTimeChanged(bool can_set_time) override;
+
   // Called when the page is ready.
   void HandleDateTimePageReady(const base::ListValue* args);
 
   // Handler to fetch the list of time zones.
   void HandleGetTimeZones(const base::ListValue* args);
 
+  // Called to show the Set Time UI.
+  void HandleShowSetDateTimeUI(const base::ListValue* args);
+
   // Updates the UI, enabling or disabling the time zone automatic detection
   // setting according to policy.
   void NotifyTimezoneAutomaticDetectionPolicy();
 
   std::unique_ptr<chromeos::CrosSettings::ObserverSubscription>
       system_timezone_policy_subscription_;
 
   // Used to listen to changes to the system time zone detection policy.
   PrefChangeRegistrar local_state_pref_change_registrar_;
 
   base::WeakPtrFactory<DateTimeHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DateTimeHandler);
 };
 
 }  // namespace settings
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DATE_TIME_HANDLER_H_