Use mojo SystemTray interfaces for both mash and classic ash

chrome/browser/ui/views/ash/chrome_browser_main_extra_parts_ash.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/views/ash/chrome_browser_main_extra_parts_ash.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/shell.h"
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 23 matching lines @@
 
 void ChromeBrowserMainExtraPartsAsh::PreProfileInit() {
   if (chrome::ShouldOpenAshOnStartup())
     chrome::OpenAsh(gfx::kNullAcceleratedWidget);
 
   if (chrome::IsRunningInMash()) {
     immersive_context_ = base::MakeUnique<ImmersiveContextMus>();
     immersive_handler_factory_ = base::MakeUnique<ImmersiveHandlerFactoryMus>();
 #if defined(OS_CHROMEOS)
     // Must be available at login screen, so initialize before profile.
+    // TODO: Always create this, even when not in mash.
     system_tray_client_ = base::MakeUnique<SystemTrayClient>();
 #endif
   }
 
 #if defined(OS_CHROMEOS)
   // For OS_CHROMEOS, virtual keyboard needs to be initialized before profile
   // initialized. Otherwise, virtual keyboard extension will not load at login
   // screen.
   keyboard::InitializeKeyboard();
 #endif
@@ skipping 17 matching lines @@
   ash::Shell::GetPrimaryRootWindowController()->ActivateKeyboard(
       keyboard::KeyboardController::GetInstance());
 }
 
 void ChromeBrowserMainExtraPartsAsh::PostMainMessageLoopRun() {
 #if defined(OS_CHROMEOS)
   system_tray_client_.reset();
 #endif
   chrome::CloseAsh();
 }