Move GetRootWindowController() to root_window_controller.h

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
index 1456defe3599a95c5024670ee1e9c56fa7ba06d0..d8348ebed4f7aa0c70d9a01223deeda053805e15 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -14,7 +14,6 @@
 #include "ash/shell.h"
 #include "ash/shell_factory.h"
 #include "ash/shell_window_ids.h"
-#include "ash/wm/property_util.h"
 #include "ash/wm/root_window_layout_manager.h"
 #include "base/bind.h"
 #include "base/command_line.h"
@@ -414,10 +413,11 @@ void DesktopBackgroundController::InstallDesktopController(
       NOTREACHED();
       return;
   }
-  GetRootWindowController(root_window)->SetAnimatingWallpaperController(
-      new internal::AnimatingDesktopController(component));
+  internal::GetRootWindowController(root_window)->
+      SetAnimatingWallpaperController(
+          new internal::AnimatingDesktopController(component));
 
-  component->StartAnimating(GetRootWindowController(root_window));
+  component->StartAnimating(internal::GetRootWindowController(root_window));
 }
 
 void DesktopBackgroundController::InstallDesktopControllerForAllWindows() {