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

ui/views/controls/menu/display_change_listener_aura.cc

Index: ui/views/controls/menu/display_change_listener_aura.cc
diff --git a/ui/views/controls/menu/display_change_listener_aura.cc b/ui/views/controls/menu/display_change_listener_aura.cc
index 1cec65148ca9d40e338e6b27dce785b2a36ff4ca..e6df5600375a0be36ffa6bbf328b1ade42651e65 100644
--- a/ui/views/controls/menu/display_change_listener_aura.cc
+++ b/ui/views/controls/menu/display_change_listener_aura.cc
@@ -2,10 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/views/controls/menu/menu_runner.h"
-
-#include "ui/aura/root_window.h"
+#include "ui/aura/window.h"
 #include "ui/aura/window_observer.h"
+#include "ui/views/controls/menu/menu_runner.h"
 #include "ui/views/widget/widget.h"
 
 namespace views {
@@ -28,7 +27,7 @@ class AuraDisplayChangeListener
 
  private:
   MenuRunner* menu_runner_;
-  aura::RootWindow* root_window_;
+  aura::Window* root_window_;
 
   DISALLOW_COPY_AND_ASSIGN(AuraDisplayChangeListener);
 };