Rename RootWindowHost to WindowTreeHost

ui/views/widget/desktop_aura/desktop_root_window_host_observer_x11.h

 // Copyright 2013 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.
 
 #ifndef UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_ROOT_WINDOW_HOST_OBSERVER_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_ROOT_WINDOW_HOST_OBSERVER_X11_H_
 
 #include "ui/views/views_export.h"
 
 namespace views {
 
 // Allows for the observation of lower level window events.
-class VIEWS_EXPORT DesktopRootWindowHostObserverX11 {
+class VIEWS_EXPORT DesktopWindowTreeHostObserverX11 {
  public:
-  virtual ~DesktopRootWindowHostObserverX11() {}
+  virtual ~DesktopWindowTreeHostObserverX11() {}
 
   // Called after we receive a MapNotify event (the X11 server has allocated
   // resources for it).
   virtual void OnWindowMapped(unsigned long xid) = 0;
 
   // Called after we receive an UnmapNotify event (the X11 server has freed
   // resources for it).
   virtual void OnWindowUnmapped(unsigned long xid) = 0;
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_ROOT_WINDOW_HOST_OBSERVER_X11_H_