Use mojo SystemTray interfaces for both mash and classic ash

ash/mus/bridge/wm_shell_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_BRIDGE_WM_SHELL_MUS_H_
 #define ASH_MUS_BRIDGE_WM_SHELL_MUS_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 44 matching lines @@
   // toplevel. |window| may be null.
   static WmWindowMus* GetToplevelAncestor(ui::Window* window);
 
   WmRootWindowControllerMus* GetRootWindowControllerWithDisplayId(int64_t id);
 
   AcceleratorControllerDelegateMus* accelerator_controller_delegate() {
     return accelerator_controller_delegate_.get();
   }
 
   // WmShell:
+  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 71 matching lines @@
 
   base::ObserverList<WmActivationObserver> activation_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShellMus);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_BRIDGE_WM_SHELL_MUS_H_