ash: Do not use MessageLoopForUI when not needed.

ash/display/mirror_window_controller.cc

 // Copyright (c) 2013 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 "ash/display/mirror_window_controller.h"
 
 #include <utility>
 
 #if defined(USE_X11)
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 
 // Xlib.h defines RootWindow.
 #undef RootWindow
 #endif
 
 #include "ash/display/cursor_window_controller.h"
 #include "ash/display/display_info.h"
 #include "ash/display/display_manager.h"
 #include "ash/display/root_window_transformers.h"
 #include "ash/display/screen_position_controller.h"
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/host/ash_window_tree_host.h"
 #include "ash/host/ash_window_tree_host_init_params.h"
 #include "ash/host/root_window_transformer.h"
 #include "ash/root_window_settings.h"
 #include "ash/shell.h"
 #include "base/strings/stringprintf.h"
+#include "base/thread_task_runner_handle.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window_delegate.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/layout.h"
 #include "ui/compositor/reflector.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/native_widget_types.h"
 
@@ skipping 332 matching lines @@
 
   host->RemoveObserver(Shell::GetInstance()->window_tree_host_manager());
   host->RemoveObserver(this);
   host_info->ash_host->PrepareForShutdown();
   reflector_->RemoveMirroringLayer(host_info->mirror_window->layer());
 
   // EventProcessor may be accessed after this call if the mirroring window
   // was deleted as a result of input event (e.g. shortcut), so don't delete
   // now.
   if (delay_host_deletion)
-    base::MessageLoop::current()->DeleteSoon(FROM_HERE, host_info);
+    base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, host_info);
   else
     delete host_info;
 }
 
 }  // namespace ash