Introdcue AshWindowTreeHost and move ash/chrome specific code in WTH to ash.

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/ash_switches.h"
 #include "ash/desktop_background/desktop_background_controller_observer.h"
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/desktop_background/desktop_background_widget_controller.h"
@@ skipping 240 matching lines @@
   Shell::RootWindowControllerList controllers =
       Shell::GetAllRootWindowControllers();
   for (Shell::RootWindowControllerList::iterator iter = controllers.begin();
     iter != controllers.end(); ++iter) {
     RootWindowController* root_window_controller = *iter;
     // In the steady state (no animation playing) the background widget
     // controller exists in the RootWindowController.
     DesktopBackgroundWidgetController* desktop_controller =
         root_window_controller->wallpaper_controller();
     if (desktop_controller) {
-      moved |= desktop_controller->Reparent(
-          root_window_controller->root_window(),
-          src_container,
-          dst_container);
+      moved |=
+          desktop_controller->Reparent(root_window_controller->GetRootWindow(),
+                                       src_container,
+                                       dst_container);
     }
     // During desktop show animations the controller lives in
     // AnimatingDesktopController owned by RootWindowController.
     // NOTE: If a wallpaper load happens during a desktop show animation there
     // can temporarily be two desktop background widgets.  We must reparent
     // both of them - one above and one here.
     DesktopBackgroundWidgetController* animating_controller =
         root_window_controller->animating_wallpaper_controller() ?
         root_window_controller->animating_wallpaper_controller()->
             GetController(false) :
         NULL;
     if (animating_controller) {
       moved |= animating_controller->Reparent(
-          root_window_controller->root_window(),
+          root_window_controller->GetRootWindow(),
           src_container,
           dst_container);
     }
   }
   return moved;
 }
 
 int DesktopBackgroundController::GetBackgroundContainerId(bool locked) {
   return locked ? kShellWindowId_LockScreenBackgroundContainer
                 : kShellWindowId_DesktopBackgroundContainer;
 }
 
 void DesktopBackgroundController::UpdateWallpaper() {
   current_wallpaper_.reset(NULL);
   ash::Shell::GetInstance()->user_wallpaper_delegate()->
       UpdateWallpaper(true /* clear cache */);
 }
 
 }  // namespace ash