Use mojo SystemTray interfaces for both mash and classic ash

ash/aura/wm_shell_aura.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_AURA_WM_SHELL_AURA_H_
 #define ASH_AURA_WM_SHELL_AURA_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 14 matching lines @@
  public:
   explicit WmShellAura(std::unique_ptr<ShellDelegate> shell_delegate);
   ~WmShellAura() override;
 
   static WmShellAura* Get();
 
   void CreatePointerWatcherAdapter();
 
   // WmShell:
   void Shutdown() override;
+  bool IsRunningInMash() const override;
   WmWindow* NewWindow(ui::wm::WindowType window_type,
                       ui::LayerType layer_type) override;
   WmWindow* GetFocusedWindow() override;
   WmWindow* GetActiveWindow() override;
   WmWindow* GetCaptureWindow() override;
   WmWindow* GetPrimaryRootWindow() override;
   WmWindow* GetRootWindowForDisplayId(int64_t display_id) override;
   const display::ManagedDisplayInfo& GetDisplayInfo(
       int64_t display_id) const override;
   bool IsActiveDisplayId(int64_t display_id) const override;
@@ skipping 63 matching lines @@
 
   bool added_display_observer_ = false;
   base::ObserverList<WmDisplayObserver> display_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShellAura);
 };
 
 }  // namespace ash
 
 #endif  // ASH_AURA_WM_SHELL_AURA_H_