Use mojo SystemTray interfaces for both mash and classic ash

chrome/browser/ui/ash/system_tray_client.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_ASH_SYSTEM_TRAY_CLIENT_H_
 #define CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CLIENT_H_
 
 #include "ash/public/interfaces/system_tray.mojom.h"
 #include "base/macros.h"
 #include "chrome/browser/chromeos/system/system_clock_observer.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
 // Handles method calls delegated back to chrome from ash. Also notifies ash of
 // relevant state changes in chrome.
+// REVIEWERS: This is now the only SystemClockObserver in chrome.
 class SystemTrayClient : public ash::mojom::SystemTrayClient,
                          public chromeos::system::SystemClockObserver {
  public:
   SystemTrayClient();
   ~SystemTrayClient() override;
 
   static SystemTrayClient* Get();
 
  private:
   // Connects or reconnects the |system_tray_| interface.
@@ skipping 19 matching lines @@
   // chromeos::system::SystemClockObserver:
   void OnSystemClockChanged(chromeos::system::SystemClock* clock) override;
 
   // System tray mojo service in ash.
   ash::mojom::SystemTrayPtr system_tray_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayClient);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CLIENT_H_