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

ui/views/widget/desktop_aura/desktop_screen_x11.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 "ui/views/widget/desktop_aura/desktop_screen_x11.h"
 
 #include <X11/extensions/Xrandr.h>
 #include <X11/Xlib.h>
 
 // It clashes with out RootWindow.
@@ skipping 169 matching lines @@
     gfx::NativeView window) const {
   // Getting screen bounds here safely is hard.
   //
   // You'd think we'd be able to just call window->GetBoundsInScreen(), but we
   // can't because |window| (and the associated RootWindow*) can be partially
   // initialized at this point; RootWindow initializations call through into
   // GetDisplayNearestWindow(). But the X11 resources are created before we
   // create the aura::RootWindow. So we ask what the DRWHX11 believes the
   // window bounds are instead of going through the aura::Window's screen
   // bounds.
-  aura::RootWindow* root_window = window->GetRootWindow();
-  if (root_window) {
+  aura::WindowEventDispatcher* dispatcher = window->GetDispatcher();
+  if (dispatcher) {
     DesktopRootWindowHostX11* rwh = DesktopRootWindowHostX11::GetHostForXID(
-        root_window->GetAcceleratedWidget());
+        dispatcher->GetAcceleratedWidget());
     if (rwh)
       return GetDisplayMatching(rwh->GetX11RootWindowBounds());
   }
 
   return GetPrimaryDisplay();
 }
 
 gfx::Display DesktopScreenX11::GetDisplayNearestPoint(
     const gfx::Point& point) const {
   for (std::vector<gfx::Display>::const_iterator it = displays_.begin();
@@ skipping 140 matching lines @@
   ProcessDisplayChange(new_displays);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 gfx::Screen* CreateDesktopScreen() {
   return new DesktopScreenX11;
 }
 
 }  // namespace views