Make GetRootWindow() return a Window instead of a RootWindow.

ash/wm/lock_state_controller.cc

Index: ash/wm/lock_state_controller.cc
diff --git a/ash/wm/lock_state_controller.cc b/ash/wm/lock_state_controller.cc
index 61172241afdbb2d45ff223d05116a5041238ef63..11b840bb678ba5d9a6578688dda2f2e532bbff0a 100644
--- a/ash/wm/lock_state_controller.cc
+++ b/ash/wm/lock_state_controller.cc
@@ -27,7 +27,7 @@ namespace ash {
 namespace {
 
 aura::Window* GetBackground() {
-  aura::RootWindow* root_window = Shell::GetPrimaryRootWindow();
+  aura::Window* root_window = Shell::GetPrimaryRootWindow();
   return Shell::GetContainer(root_window,
       internal::kShellWindowId_DesktopBackgroundContainer);
 }
@@ -156,11 +156,12 @@ LockStateController::LockStateController()
       shutdown_after_lock_(false),
       animating_lock_(false),
       can_cancel_lock_animation_(false) {
-  Shell::GetPrimaryRootWindow()->AddRootWindowObserver(this);
+  Shell::GetPrimaryRootWindow()->GetDispatcher()->AddRootWindowObserver(this);
 }
 
 LockStateController::~LockStateController() {
-  Shell::GetPrimaryRootWindow()->RemoveRootWindowObserver(this);
+  Shell::GetPrimaryRootWindow()->GetDispatcher()->RemoveRootWindowObserver(
+      this);
 }
 
 void LockStateController::SetDelegate(LockStateControllerDelegate* delegate) {