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

ash/wm/window_cycle_controller_unittest.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/wm/window_cycle_controller.h"
 
 #include <algorithm>
 
 #include "ash/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_shell_delegate.h"
 #include "ash/wm/window_cycle_list.h"
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/env.h"
+#include "ui/aura/root_window.h"
 #include "ui/aura/test/test_windows.h"
 #include "ui/aura/window.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/screen.h"
 
 namespace ash {
 
 namespace {
 
 using aura::test::CreateTestWindowWithId;
@@ skipping 405 matching lines @@
   controller->HandleCycleWindow(WindowCycleController::FORWARD, true);
   EXPECT_TRUE(wm::IsActiveWindow(window2.get()));
 
   controller->HandleCycleWindow(WindowCycleController::FORWARD, true);
   EXPECT_TRUE(wm::IsActiveWindow(window0.get()));
 }
 
 }  // namespace
 
 }  // namespace ash