ash: Do not use MessageLoopForUI when not needed.

ash/system/tray/system_tray_bubble.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/system/tray/system_tray_bubble.h"
 
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "ash/system/tray/tray_bubble_wrapper.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_popup_item_container.h"
-#include "base/message_loop/message_loop.h"
+#include "base/thread_task_runner_handle.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/gfx/canvas.h"
 #include "ui/views/layout/box_layout.h"
 #include "ui/views/view.h"
 #include "ui/views/widget/widget.h"
 
 using views::TrayBubbleView;
@@ skipping 17 matching lines @@
 // the animation.
 class AnimationObserverDeleteLayer : public ui::ImplicitAnimationObserver {
  public:
   explicit AnimationObserverDeleteLayer(ui::Layer* layer)
       : layer_(layer) {
   }
 
   ~AnimationObserverDeleteLayer() override {}
 
   void OnImplicitAnimationsCompleted() override {
-    base::MessageLoopForUI::current()->DeleteSoon(FROM_HERE, this);
+    base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, this);
   }
 
  private:
   scoped_ptr<ui::Layer> layer_;
 
   DISALLOW_COPY_AND_ASSIGN(AnimationObserverDeleteLayer);
 };
 
 }  // namespace
 
@@ skipping 253 matching lines @@
     // 2 items, which are the bottom header row and the one just above it.
     bubble_view_->AddChildView(new TrayPopupItemContainer(
         item_views[i], is_default_bubble,
         is_default_bubble && (i < item_views.size() - 2)));
   }
   if (focus_view)
     focus_view->RequestFocus();
 }
 
 }  // namespace ash