CrOS: Enable threaded UI compositor by default.

ash/desktop_background/desktop_background_view.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/desktop_background/desktop_background_view.h"
 
 #include <limits>
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_controller.h"
@@ skipping 43 matching lines @@
  private:
   // Overridden from ui::ImplicitAnimationObserver:
   virtual void OnImplicitAnimationsScheduled() OVERRIDE {
     if (is_initial_animation_) {
       GetRootWindowController(root_window_)->
           HandleInitialDesktopBackgroundAnimationStarted();
     }
   }
 
   virtual void OnImplicitAnimationsCompleted() OVERRIDE {
-    DCHECK(desktop_widget_);
     GetRootWindowController(root_window_)->HandleDesktopBackgroundVisible();
     ash::Shell::GetInstance()->user_wallpaper_delegate()->
         OnWallpaperAnimationFinished();
     // Only removes old component when wallpaper animation finished. If we
     // remove the old one before the new wallpaper is done fading in there will
     // be a white flash during the animation.
     if (root_window_->GetProperty(kAnimatingDesktopController)) {
       DesktopBackgroundWidgetController* controller =
           root_window_->GetProperty(kAnimatingDesktopController)->
               GetController(true);
@@ skipping 144 matching lines @@
   settings.AddObserver(new ShowWallpaperAnimationObserver(
       root_window, desktop_widget,
       wallpaper_delegate->ShouldShowInitialAnimation()));
   desktop_widget->Show();
   desktop_widget->GetNativeView()->SetName("DesktopBackgroundView");
   return desktop_widget;
 }
 
 }  // namespace internal
 }  // namespace ash