ash: Do not use MessageLoopForUI when not needed.

ash/display/window_tree_host_manager.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 "ash/display/window_tree_host_manager.h"
 
 #include <algorithm>
 #include <cmath>
 #include <map>
 #include <utility>
@@ skipping 15 matching lines @@
 #include "ash/screen_util.h"
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/wm/coordinate_conversion.h"
 #include "ash/wm/window_util.h"
 #include "base/command_line.h"
 #include "base/stl_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/thread_task_runner_handle.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_property.h"
 #include "ui/aura/window_tracker.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/ime/input_method_factory.h"
 #include "ui/compositor/compositor.h"
@@ skipping 589 matching lines @@
 
 void WindowTreeHostManager::DeleteHost(AshWindowTreeHost* host_to_delete) {
   ClearDisplayPropertiesOnHost(host_to_delete);
   RootWindowController* controller =
       GetRootWindowController(GetWindow(host_to_delete));
   DCHECK(controller);
   controller->MoveWindowsTo(GetPrimaryRootWindow());
   // Delete most of root window related objects, but don't delete
   // root window itself yet because the stack may be using it.
   controller->Shutdown();
-  base::MessageLoop::current()->DeleteSoon(FROM_HERE, controller);
+  base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, controller);
 }
 
 void WindowTreeHostManager::OnDisplayRemoved(const gfx::Display& display) {
   AshWindowTreeHost* host_to_delete = window_tree_hosts_[display.id()];
   CHECK(host_to_delete) << display.ToString();
 
   // When the primary root window's display is removed, move the primary
   // root to the other display.
   if (primary_display_id == display.id()) {
     // Temporarily store the primary root window in
@@ skipping 177 matching lines @@
   SetDisplayPropertiesOnHost(ash_host, display);
 
 #if defined(OS_CHROMEOS)
   if (switches::ConstrainPointerToRoot())
     ash_host->ConfineCursorToRootWindow();
 #endif
   return ash_host;
 }
 
 }  // namespace ash