Reland "Fix wallpaper fade animation flashing problem"

ash/desktop_background/desktop_background_controller.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_controller.h"
 
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/shell.h"
 #include "ash/shell_factory.h"
 #include "ash/shell_window_ids.h"
@@ skipping 11 matching lines @@
 DesktopBackgroundController::DesktopBackgroundController() :
   desktop_background_mode_(BACKGROUND_IMAGE) {
 }
 
 DesktopBackgroundController::~DesktopBackgroundController() {
 }
 
 void DesktopBackgroundController::SetDesktopBackgroundImageMode() {
   internal::RootWindowLayoutManager* root_window_layout =
       Shell::GetInstance()->root_window_layout();
-  if (root_window_layout->background_widget())
-    root_window_layout->background_widget()->Hide();
   int index = Shell::GetInstance()->user_wallpaper_delegate()->
       GetUserWallpaperIndex();
   root_window_layout->SetBackgroundLayer(NULL);
-  root_window_layout->SetBackgroundWidget(
-      internal::CreateDesktopBackground(GetWallpaper(index),
-                                        GetWallpaperInfo(index).layout));
+  internal::CreateDesktopBackground(GetWallpaper(index),
+                                    GetWallpaperInfo(index).layout);
   desktop_background_mode_ = BACKGROUND_IMAGE;
 }
 
 void DesktopBackgroundController::SetDesktopBackgroundSolidColorMode() {
   // Set a solid black background.
   // TODO(derat): Remove this in favor of having the compositor only clear the
   // viewport when there are regions not covered by a layer:
   // http://crbug.com/113445
   Shell* shell = Shell::GetInstance();
   ui::Layer* background_layer = new ui::Layer(ui::LAYER_SOLID_COLOR);
   background_layer->SetColor(SK_ColorBLACK);
   shell->GetContainer(internal::kShellWindowId_DesktopBackgroundContainer)->
       layer()->Add(background_layer);
   shell->root_window_layout()->SetBackgroundLayer(background_layer);
   shell->root_window_layout()->SetBackgroundWidget(NULL);
   desktop_background_mode_ = BACKGROUND_SOLID_COLOR;
 }
 
 }  // namespace ash