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

ash/shell/window_watcher.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 "ash/shell/window_watcher.h"
 
 #include "ash/display/display_controller.h"
 #include "ash/launcher/launcher.h"
 #include "ash/launcher/launcher_item_delegate_manager.h"
 #include "ash/launcher/launcher_model.h"
@@ skipping 18 matching lines @@
 
   virtual void OnWindowAdded(aura::Window* new_window) OVERRIDE {
     new_window->AddObserver(watcher_);
   }
 
   virtual void OnWillRemoveWindow(aura::Window* window) OVERRIDE {
     DCHECK(window->children().empty());
     window->RemoveObserver(watcher_);
   }
 
-  void RootWindowAdded(aura::RootWindow* root) {
+  void RootWindowAdded(aura::Window* root) {
     aura::Window* panel_container = ash::Shell::GetContainer(
         root,
         internal::kShellWindowId_PanelContainer);
     panel_container->AddObserver(watcher_);
 
     aura::Window* container =
         Launcher::ForWindow(root)->shelf_widget()->window_container();
     container->AddObserver(this);
     for (size_t i = 0; i < container->children().size(); ++i)
       container->children()[i]->AddObserver(watcher_);
@@ skipping 93 matching lines @@
       id_to_window_.erase(i);
       break;
     }
   }
 }
 
 void WindowWatcher::OnDisplayBoundsChanged(const gfx::Display& display) {
 }
 
 void WindowWatcher::OnDisplayAdded(const gfx::Display& new_display) {
-  aura::RootWindow* root = Shell::GetInstance()->display_controller()->
+  aura::Window* root = Shell::GetInstance()->display_controller()->
       GetRootWindowForDisplayId(new_display.id());
   workspace_window_watcher_->RootWindowAdded(root);
 }
 
 void WindowWatcher::OnDisplayRemoved(const gfx::Display& old_display) {
   // All windows in the display has already been removed, so no need to
   // remove observers.
 }
 
 }  // namespace shell
 }  // namespace ash