mash: Add SystemTrayClient interface, use to show date settings

ash/mus/system_tray_delegate_mus.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 ASH_MUS_SYSTEM_TRAY_DELEGATE_MUS_H_
 #define ASH_MUS_SYSTEM_TRAY_DELEGATE_MUS_H_
 
 #include "ash/common/system/tray/default_system_tray_delegate.h"
 #include "ash/public/interfaces/system_tray.mojom.h"
 #include "base/i18n/time_formatting.h"
@@ skipping 10 matching lines @@
                               public mojom::SystemTray {
  public:
   SystemTrayDelegateMus();
   ~SystemTrayDelegateMus() override;
 
   static SystemTrayDelegateMus* Get();
 
  private:
   // SystemTrayDelegate:
   base::HourClockType GetHourClockType() const override;
+  void ShowDateSettings() override;
 
   // mojom::SystemTray:
+  void SetClient(mojom::SystemTrayClientPtr system_tray_client) override;
   void SetUse24HourClock(bool use_24_hour) override;
 
+  // The client is usually chrome browser.
+  mojom::SystemTrayClientPtr system_tray_client_;
+
   // 12 or 24 hour display.
   base::HourClockType hour_clock_type_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayDelegateMus);
 };
 
 }  // namespace ash
 
 #endif  // ASH_MUS_SYSTEM_TRAY_DELEGATE_MUS_H_